PCM-ECM Archives • LS Engine DIY

Gen III LS PCM Conversion Upgrades: Projects, Lessons and Strategies

LS Engine DiY — Tue, 17 Feb 2015 00:59:04 +0000

For years now, enthusiasts have been retrofitting early project cars with LS-series engines and Gen III PCM conversions. The available features (cable or electronic throttle, cruise control, forced induction support, and so on) make the Gen III PCMs highly desirable for nearly any conversion.

The following projects are fine examples of Gen III control systems for small-block engines, turbocharged V-8 and V-6 engines, LT1 engines, and big-block engines.

Project 1: 24x Small-Block Chevy in a 1933 Willys

This 1933 Willys was built and owned by Bill Adam. The car originally had a 5.7L TPI engine from a 1987 Camaro Z28 and an ECM from a 1990 Corvette. Bill chose to upgrade the ECM to the GM# 12200411 PCM for greater tune-ability and a future 4L60E transmission install.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

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This is Bill Adam’s 1933 Willys. I met Bill in 2002 when he and his son, Troy, heard there was a guy down the road (me) playing with TPI engines. Bill is a retired toolmaker and fabricated just about everything in this car. He was one of the first in town to install a fuel-injected V-8 engine in a street rod. When I first met Bill, his Willys had an original 1987 5.7L TPI engine with aftermarket wire harness and an ECM (GM# 1227727) from a 1990 Corvette. The Willys ran great, but after seeing some of the newer technology I was playing with, Bill couldn’t leave well enough alone.

GM 4x Vortec Small-Block System

In 2006, Bill and I worked together to upgrade the ECM to a 2002 PCM (GM# 12200411) for single coil and distributor operation using a 1996–2002 ignition system and 2002 Express Van calibration file. In hot rodder fashion, the electronics upgrade turned into a heads-up upgrade, including ported aftermarket heads, LT4 hot cam, and TPIS Mini Ram intake manifold. Ultimately the conversion to the GM truck ignition system with this PCM was a failure due to a persistent corrosion problem within (several different styles of) the Vortec distributor.

EFI Connection 24x Small-Block System

Bill was ready to throw in the towel and go back to the TPI ECM. But by then, the prototyping of an EFI Connection24x crankshaft reluctor for small-block engines was nearly complete. So, Bill’s Willys became the first vehicle to receive a 24x conversion (the second was my S10 Wildside pickup).

Bill fabricated his own ignition coil mounts by drilling holes through a set of aftermarket die-cast aluminum valve covers and attaching threaded posts to screws from the back side of each valve cover. These LS1/LS6 ignition coils don’t allow much room for oil fill, PCV valve, or breather holes. An alternative choice for better clearance is a set of GM# 12573190 ignition coils.

This was the first engine to receive EFI Connection’s 24x conversion. At the time of prototyping, the 1996-newer Vortec V-8 plastic timing cover was the only choice for this application. Due to a slight mismatch of timing cover sealing surfaces between early and late engine blocks, Bill chose to apply JB Weld to the face of the block to extend the seal surface. The TPIS billet-aluminum SBC timing cover now resolves this sealing issue.

Mounting the ignition coils on the valve covers is not for everyone, but this engine bay offers no other room for cleanly mounting the eight coils.

Removing the high voltage from the Vortec distributor, we only needed the camshaft position signal it provides. Moisture or no moisture within the distributor cap, Bill no longer had to worry about ignition problems related to the Vortec distributor. The 4x Vortec small-block crankshaft reluctor was removed and replaced with the first 24x small-block crankshaft reluctor.

Timing Cover

A problem with any crankshaft reluctor installation on an engine that did not originally have a crankshaft reluctor (1995-older) is that General Motors changed the timing cover sealing surface just enough that the 1996- newer plastic Vortec timing covers leak. Although TPIS has since resolved this problem with a machined billet aluminum timing cover, Bill cleaned the face of this 1987 block to apply JB Weld to the trouble areas, ground the new surfaces flat, and then generously applied red RTV sealant to protect against oil leaks.

For the hassle and oil leak risk involved, you are better off buying the TPIS billet-aluminum timing cover and being done with it. TPIS designed their billet-aluminum small-block timing cover for original crankshaft sensor placement, making this beautiful timing cover a direct bolt on for 1996-newer small-block engines as well.

TPIS designed and manufactures this beautiful billet-aluminum timing cover for small-block Chevy engines. This timing cover eliminates oil leak issues of the 1996-newer Vortec V-8 timing cover when used with a 1995 or older small-block Chevy engine.

Speed Density

Bill initially chose the 1990 TPI ECM because it offered speed-density operation. The 1990–1992 TPI ECMs use a MAP sensor to determine how much fuel to deliver. With tight clearance ahead of the throttle body, and a mechanical fan, a MAF sensor was not possible in this engine bay. The 1996-newer GM fuel management systems use both a MAF and a MAP but the MAF sensor is often eliminated and the PCM is programmed to rely on the MAP sensor for fuel delivery.

Ignition Coil Selection

Bill chose to use LS1 ignition coils (simply because they were available). Some owners unnecessarily get caught up with ignition coil selection. General Motors has used five types of ignition coils (see Chapter 6). Any set of eight ignition coils can be used interchangeably. In fact, among LS-series engines, all ignition coil wire harnesses match every LS-series engine wire harness.

Be aware that the PCM calibration has dwell settings that may need to be adjusted if you use a different set of eight ignition coils. EFI Connection uses the very common GM# 12573190 ignition coils because they fit best on the small-block/LT1 valve covers to allow clearance for oil fill cap, PCV valve, and breather.

DTCs on Startup

Production GM vehicles contain solenoids, relays, sensors, and on-board modules not used in most conversion projects. Upon initial startup of your Gen III PCM conversion, you may notice DTCs that have set related to something that is not used in your vehicle.

Using a base calibration from a 2002 LS1 Camaro with a 4L60-E transmission, the Willys set more than 30 DTCs immediately following the first engine startup. DTCs related to the 4L60-E transmission, emissions equipment, air conditioning, cooling fans, and alternator (that covers just about all of them) can be disabled because the LS1 PCM is not controlling or monitoring this equipment for this vehicle. The mass airflow DTC (P0102) is actually required for DTC processing for speed density operation, but the calibration is set to never illuminate the MIL. It is “normal” for a conversion and clearly explained in EFILive documentation.

VATS Bypass Modules

Almost daily, enthusiasts throw money away by purchasing VATS bypass modules. I quickly found one of these modules on eBay advertising, “Normally it costs between $150 and $300 to have this feature deleted from the PCM. By using our module you accomplish the same function for less and you won’t have to ship your PCM/ ECM to have it reprogrammed.” A VATS bypass module is often purchased during the parts gathering phase of a project and then not used.

The problem with using a bypass module is that the PCM still requires programming to disable other functions specific to the original car. No matter how well-built these modules are, they do nothing more than allow the engine to run so that you can be greeted with an MIL that indicates you need your PCM reprogrammed.

The PCM calibration requires a few changes beyond disabling VATS. Avoid the VATS bypass module and let your tuner disable VATS in the PCM calibration while making other necessary changes.

700R4 Transmission

Bill and I began with a PCM calibration from a vehicle with a 4L60-E transmission so the idle table values would be appropriate for the 700R4 automatic transmission in the car. The PCM immediately sets DTCs related to the 4L60-E transmission. We disabled these within the PCM calibration using EFILive tuning software. This is an appropriate step as they are disabled in a PCM calibration from a manual transmission vehicle. Had General Motors released an LS-series vehicle with the 700R4 transmission, they too would have disabled these DTCs. Bill and I had the foresight to build the engine wire harness to support a 4L60-E transmission.

General Motors appropriately enables (and disables) DTCs for production vehicles according to the features specific to each vehicle. A Gen III LS PCM conversion requires certain DTCs to be disabled according to the features being used in the retrofit vehicle. The first engine startup revealed this list of DTCs that were later disabled (turned off). These DTCs are appropriate for the 2002 Camaro LS1/4L60E, but not for a 1933 Willys.

Cruise Control

Adding cruise control to the Willys was an afterthought. The installation was completed; start to finish, over the better part of a Saturday. We scored a used 1998 LS1 Camaro cruise control module on eBay for about $50 and pulled a brake switch from a 1996 LT1 brake pedal assembly that was lying around. The addition of cruise control set us back about $75 and several hours of labor. The Willys required a slight variation on the typical cruise control wiring (see Chapter 14).

First, Bill prototyped a throttle body linkage adapter for the TPI throttle body. This was the most difficult part of the installation because the cruise control cable was designed for an LS1 engine throttle bracket and throttle body. This adapter can be reworked for a better, and cleaner, installation.

Bill identified a stealthy location for the cruise control module beneath the driver’s seat and on the bottom side of the floor. The F-Body cable is plenty long enough to mount the cruise control module out of sight.

Bill had to make a custom throttle cable adapter to receive the 1998 Camaro Z28 cruise control cable. Here a prototype is shown during installation.

A new wire harness for the cruise control module is shown on the floor next to Bill as he is routing the wires up the pillar in front of the door.

This wire schematic represents the implementation of a 1998 Camaro Z28 cruise control module into the Willys. Notice the PCM’s secondary VSS output was used to provide a 4,000 pulse-per-mile signal to the cruise control module as the primary VSS output was already used for the speedometer. The 1998 Camaro Z28 cruise control module does not require the cruise engaged status or cruise inhibit signals.

Although a 1996 Camaro/Firebird brake switch was installed for proper cruise control signals, many other GM brake switches provide the same signals.

To satisfy the cruise control module’s 4,000 pulse-per-mile VSS input requirement, a terminated wire was inserted into cavity 49 of the red PCM connector (PCM secondary VSS output).

This early GM steering column contained a cruise control set/coast switch only. There was no provision for the accelerate/resume functions.

The 1998 Camaro Z28 cruise control module fit comfortably between the frame rails of this Willys. The Camaro/Firebird cruise control cable is much longer than the GM truck cables. This cable length was ideal for hiding the cruise control module under the vehicle.

With the PCM’s secondary VSS output circuit now attached to the cruise control module’s 4,000-pulse-per-mile VSS input, a calibration change was made to set the PCM’s pulse count to 4,000.

While we could have used just about any GM brake switch from a vehicle with cruise control, we had a 1996 F-Body brake switch that fit nicely within the tight space of the dash. We tapped into the stop lamp circuit and TCC brake signal circuit to satisfy the cruise control module’s brake switch signal requirements. Bill used a steering column from an early GM vehicle with cruise control. The multi-function lever (turn signal and cruise control switch lever) only had the set/coast feature, so we wired the cruise ON/OFF to switched 12V ignition, ignoring the resume/accel feature.

The cruise control module requires a 4,000 pulse-per-mile VSS signal, so we looked to the LS1 PCM. The PCM’s primary VSS output was already being used for the speedometer (red connector, cavity 50, green/white wire), so we used the PCM’s secondary VSS output wire at the red connector, cavity 49. The final step was to change the PCM’s secondary VSS output signal to 4,000 pulses per mile using EFILive tuning software.

Conclusion

Bill’s 1933 Willys is a fine example of a Gen III PCM bringing modern fuel injection, tuning, and additional nice-to-have features (such as cruise control) to an early street rod. The only improvement left for the Willys is a 4L60-E transmission upgrade. The 700R4 has seen better days and Bill is already looking forward to the drivability improvements after a 4L60-E installation.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

Project 2: Twin-Turbo Small-Block Chevy in a 1998 GMC Truck

Jeff Jones’ Twin-Turbo 1998 GMC truck. (Photo Courtesy Jeff Jones)

Jeff Jones is the owner of a unique 1998 GMC Sierra. Although his professional automotive day job is as a Lexus technician, his automotive hobby includes GM engine performance. Looking for more performance from his 5.0L Vortec engine, he went to the salvage yard to source two turbos for a little added “boost.” The plastic Vortec intake manifold was problematic for several reasons, including the inability to properly size fuel injectors for the additional demands of using two turbos. A Ram Jet 350 intake manifold was a direct fit to the 5.0L Vortec engine and allowed for external fuel injectors, a forward-facing throttle body, and better airflow than the original intake manifold. The next issue was to address the limitations of the 1996–2000 Vortec “black box” PCM that General Motors designed to power the truck.

PCM Considerations

Jeff’s twin-turbo build required a better PCM than was in the car. The truck’s original black box PCM is not capable of reading boost or MAP sensor values above 105 kpa. He dismissed aftermarket ECUs with a hunch that a newer GM PCM may allow for the rest of his truck (gauges, transmission, air conditioning, etc.) to remain fully functional. Jeff knew that the Vortec 5.0L engine in his GMC was used through 2002 in the Chevy Express Van and that the 2002 Express Van used the same PCM (GM# 12200411) that is used with 2002 LS-series engines.

EFILive COS forced-induction table showing MAP above 105 kpa.

LS1 PCM connectors, retainers, dress covers, terminals, and removal tool.

With the buzz on Internet message forums discussing LS1 vehicles being tuned for forced induction while using the original GM PCM, he had a promising direction forward. Thanks to EFILive, the GM PCM can be loaded with a custom OS to fully support forced induction.

Repinning the Engine Wire Harness

While wiring in a new PCM may seem like an enormous task, General Motors has made this rather easy by using the same connector terminals for 1996–2000 truck PCMs and the 2001–2002 GM# 12200411 PCM. The connector family and series are Delphi Micro-Pack 100W. Although the connectors are different, the terminals are interchangeable. All that is required is a terminal removal tool (or your fingernail), wiring diagrams, and a little time.

Jeff has been helping truck owners repin their black box PCMs for the newer PCM (GM# 12200411) for years through a well-documented repin guide. The Gen III PCMs require two 80-cavity Micro-Pack 100W connectors; each connector uses two colored and indexed retainers. This PCM requires two blue retainers and two red retainers.

GM# 12200411 LS1 PCM installed in the truck. (Photo Courtesy Jeff Jones)

Instrument cluster removed. (Photo Courtesy Noel Schnell)

The 1996–2000 PCM is located on the driver-side fender in the engine bay. The engine wire harness is easily accessed and serviceable when disconnected from the PCM. The Vortec black box PCM uses four (sometimes five) connectors.

The new PCM fits nicely in the location of the original black box PCM. The engine wire harness is repinned, one wire at a time, with the two 80-cavity LS-series PCM connectors. If you take your time, you can make the harness rework of the new PCM look as if it has always been there.

Gear Select Switch

In an automatic transmission vehicle, the PCM needs to know when the transmission is in park or neutral (P/N), or in gear. Manual transmission vehicles do not have a gear select switch.

In 1996–2000 GM trucks, the automatic transmissions have a gear select switch mounted on the side of the transmission case. The four-gear select switch wires are routed to the instrument cluster. Jeff chose to splice into these four wires from inside the truck to avoid corrosion and weather-related issues that can occur if the splices are made under the truck.

Because the first use of this PCM (GM# 12200411) in this 1998 GMC truck was with a calibration from a 2002 Express Van (4x crankshaft reluctor), the calibration’s gear select switch type was already set to PRNDL (because the 2002 Express Van has a gear select switch on the side of the transmission).

Gear select switch type.

After the 24x conversion, Jeff began with a 2002 LS1 Camaro/Firebird calibration and had to change the gear select switch type from P/N Switch to PRNDL. The LS1 Camaro and Firebird do not use a gear select switch on the side of the transmission since a P/N switch is in the center console that applies a single ground signal to the PCM (blue connector, pin 34) to indicate P/N.

An alternative after a 24x conversion is to begin with a calibration from an LS-series truck because the calibration is already set to the gear select switch type of PRNDL, as LS-series trucks have a gear select switch mounted on the side of the transmission case.

Electric Fans

Dual electric fans from a 2002 LS1 Firebird were installed after the PCM conversion. The Gen III PCMs can control up to two electric fans. The PCM does not supply power and ground for the fans, it supplies the ground trigger to the fan relays. The fan relays supply the power and ground for the fans. A quick trip to the local salvage yard sourced three relays and connectors for the wiring involved. By using the three relays, as is done in the LS1 Camaro/Firebird, the PCM can command low-/ high-speed operation of the two electric fans. (See Chapter 9 for more about electric fan operation.)

After the dual electric fan installation, Jeff added the Camaro/Firebird three-wire A/C pressure sensor for proper operation of the electric fans when the A/C was on. Now the cooling fans cycle properly to meet the demands of the A/C system. (See Chapter 11 for more information about A/C operation.)

The LS1 Firebird electric fans are mounted neatly behind the radiator.

4x Crankshaft Signal: Single Coil and Distributor

On a Vortec small-block engine, the CKP sensor signal output is 4x and CMP sensor signal output is 1x. The ignition system for all Vortec small-block engines is single coil and distributor. Although the ignition system remained the same, the new PCM brought the benefits of forced induction support, electric fan operation, engine speed beyond 5,800 rpm, and popular tuning software support. After all, locating a chassis dyno facility that is fluent with the LS-series PCMs is rather easy.

24x Crankshaft Signal: Coil-Per-Cylinder Ignition

Several years after the PCM conversion, this 5.0L Vortec engine received an EFI Connection 24x crankshaft reluctor and new crankshaft sensor. Having already repinned the engine wire harness at the PCM, all that had to be done was add 10 ignition coil control wires and use the 12V switched ignition and ground wires from the original ignition module and coil wiring to power the eight LS ignition coils. Rather than mount the ignition coils on the valve covers, a bracket was made to mount them on the firewall.

Throttle Swap

Jeff has been gathering parts for a swap from cable throttle to electronic throttle. With a 24x crankshaft reluctor in the engine, he may install a 2003-newer Gen III PCM. Electronic throttle equipment is plentiful in 2003-newer LS-series trucks, but he will run into a snag with electric fan operation while the A/C is on because the 2003- newer GM trucks eliminated the 12V A/C request to the PCM.

A workaround is to activate the electric fan relays from the A/C control switch (and disable the resulting electric fan DTCs in the PCM calibration).

To keep PCM-controlled electric fan operation while the A/C is on, either LS1/LS6 Corvette electronic throttle equipment or 1999–2002 GM truck electronic throttle equipment may be used while retaining the PCM (GM# 12200411). (See Chapter 8 for more information about electronic throttle equipment.)

Regardless of his choice, the Ram Jet 350 intake manifold accepts any Gen III throttle body and the cruise control switches in the steering column multifunction lever integrate seamlessly with any Gen III TAC module. With several electronic pedal assembly options, a custom mount and possible alterations to the pedal length may be required to properly locate the accelerator pedal pad.

Final Thoughts

The PCM swap was the foundation for every modification that has been done to Jeff’s truck. He considers this project and PCM-related upgrades to be one of the most educational and fun things he has ever done. From Internet message forums, Jeff has learned from people around the world with this same passion, and they shared information and creative ideas. Through this DIY project, he has created unexpected friendships that help to keep this passion alive.

Engine bay. (Photo Courtesy Jeff Jones)

Engine bay showing electric fans. (Photo Courtesy Jeff Jones)

Ignition coils on firewall. (Photo Courtesy Jeff Jones)

Front of truck with “LEX TEK” plate. (Photo Courtesy Jeff Jones)

I met Jeff at his home while en route to the 2009 Car Craft Summer Nationals event. Sharing his genuine passion for GM engine management fuels my flame for this exciting hobby. Don’t let the Lexus technician title fool you; Jeff represents GM performance through and through!

Project 3: Turbo 4.3L V-6 3x Conversion

Syclone/Typhoon lower intake manifold with six injectors.

Fuel injection for GM’s popular 4.3L V-6 engines was introduced in the 1980s with a TBI unit on the top of the engine’s intake manifold. These TBI units use two fuel injectors to distribute fuel in a central location within the intake manifold. Engine vacuum pulls the air/ fuel mixture into each cylinder for combustion. These early 4.3L engines are controlled by ECMs designed to be used with the two TBI injectors.

The 1991 GMC Syclone received the first 4.3L V-6 engine to feature multi-port injection; it had six individual fuel injectors for fuel delivery into each cylinder head intake runner. This improved method of fuel delivery required a new ECM with internal drivers capable of operating the six high-impedance fuel injectors. Although six fuel injectors are used, the ECM has only two injector drivers to run a batch fi re mode (one bank of three injectors at a time). Sequential fire injection was not available for the GMC Syclone or GMC Typhoon.

The 1991 GMC Syclone and 1992–1993 GMC Typhoon do not share the ECM or ignition system with any other 4.3L V-6 engine application. The unique requirement for forced induction, a turbocharger fitted on these 4.3L V-6 engines, was an ECM and calibration capable of controlling the engine’s six fuel injectors and spark advance while under boost (2-bar) conditions. The typical 4.3L V-6 ECM of those days was not designed to be used with this turbocharged engine.

With upgraded engine components (and more boost), 4.3L V-6 owners have gone to the aftermarket to install new (and expensive) fuel management systems for greater tune-ability and control of their powerplant. Unfortunately, aftermarket systems may lack support for the vehicle’s gauges, cruise control, and transmission torque converter lockup control, thus requiring additional aftermarket solutions that only add to the expense of an upgraded fuel management and ignition system.

Gen III PCM

Here is great news for the 4.3L V-6: General Motors has inexpensive production parts available to use the Gen III PCM with any 4.3L V-6 engine. The 2001–2002 PCM (GM# 12200411) was used with both LS-series V-8 engines and the 4.3L V-6 engines found in S-series trucks and vans. These engines are fitted with the 1996-newer 3x crankshaft reluctor and single coil and distributor Vortec ignition system. The same tuning software, such as EFILive, is used with this PCM, regardless of V-6 or V-8 calibration. Other tuning benefits, such as custom operating systems for 2- and 3-bar MAP support, are conveniently included.

GM’s 3x crankshaft reluctor for Vortec V-6 engines is shaped to allow clearance for only a single roller timing chain. Production GM engines use a single roller timing chain, so if upgrading to a double roller timing chain, EFI Connection’s 3x billet-steel crankshaft reluctor is required for reluctor-to-timing chain clearance.

The 1996 4.3L Vortec V-6 engine was updated with an upper balance shaft. The changes to the face of the engine block required a new, and taller, timing cover. This timing cover made provision for the CKP sensor that is used to receive an engine position signal from the 3x crankshaft reluctor.

ECM, distributor, and ignition coil.

3x GM reluctor and 3x EFI Connection reluctor.

Plastic Vortec timing cover and TPIS billet small-block timing cover.

Those with an early 4.3L V-6 are not able to use the GM plastic Vortec timing cover because the upper portion of the cover does not seal to the early engine block. Fortunately the early 4.3L V-6 engines share the same timing cover as Gen I small-block engines. For CKP sensor provision for early 4.3L engines, the TPIS billet-aluminum small-block timing cover provides the best fitment while properly sealing to the face of the engine block.

The GM# 12200411 PCM controls the six fuel injectors in sequential fire (not batch fire) mode. This means individual control of the fuel injectors. With the requirement of six fuel injectors, this newer PCM cannot be used with TBI units.

Early 4.3L TBI engines must receive a multi-port injection intake manifold upgrade so that six fuel injectors may be used. This requirement may be filled by sourcing a used Syclone or Typhoon intake manifold, aftermarket or custom manifold, or upgrading to Vortec cylinder heads and a production GM intake manifold. An attractive option for 4.3L engines using Vortec cylinder heads is the 4.3L marine manifold because it features external fuel injectors and a Gen III 3-bolt type throttle body.

The Syclone/Typhoon, Vortec truck, and LS-series throttle body TPS and IAC engines are directly compatible with this PCM. In fact, so are the ECT, IAT, and MAP sensors used with these V-6 and V-8 engines. The only remaining sensors to add are knock sensors, heated O2 sensors, optional MAF sensor, CMP sensor, and CKP sensor.

Single Coil and Distributor Ignition

The GM# 12200411 PCM was only used with the 4.3L V-6 engines in a single coil and distributor configuration. General Motors wrote the calibration software to expect 3x crankshaft and 1x camshaft signals for engine operation. This PCM uses the 3x crankshaft signal (and other engine sensor inputs) to control the ignition spark advance through the Vortec ignition module and single coil.

It may seem that by providing a higher-resolution crankshaft signal (such as a 24x LS-series crankshaft signal), the PCM controls one coil per cylinder but it simply does not work that way. GM’s 24x encoded signal is mapped for V-8 engines only. Had General Motors released a PCM calibration that supported coil-per-cylinder ignition for the V-6, an appropriate crankshaft reluctor with increased tooth count (higher resolution) could be installed to eliminate single coil and distributor ignition. What General Motors has provided, however, is no disappointment.

Tuning software, such as EFILive, delivers the same tuning benefi ts that sell us on the use of the Gen III PCM for LS-series engines as it does for V-6 engines. Through the same calibration tables and parameters, the same tuning software and hardware, and the same tuning techniques, this PCM is a fantastic engine controller for any 4.3L V-6 engine.

Iron marine intake manifold.

Vortec ignition module and coil.

Intake Manifold

Vortec cylinder heads are plentiful in the boneyards and offer excellent performance gain compared to the early 4.3L cylinder heads. The lower Syclone and Typhoon intake manifold may be modified to accommodate the raised intake runners of the Vortec cylinder heads. Rather than machine the Syclone or Typhoon intake manifold for the Vortec head bolt pattern, the Vortec heads can be drilled for the early 4.3L V-6 bolt pattern to create a better seal and clamping force.

3x Crankshaft Reluctor

The 3x crankshaft reluctor installs on the crankshaft and is firmly held in place between the crankshaft timing sprocket and crankshaft balancer. GM’s 3x crankshaft reluctor fully seats against the crankshaft timing sprocket only when using a single roller timing chain. Double roller timing chain installations require EFI Connection’s 3x crankshaft reluctor.

EFI Connection’s 3x crankshaft reluctor, double roller timing chain, and front Engine.

Vortec Distributor Assembly

The 1996-newer 4.3L V-6 distributor assembly installs in the traditional distributor location and is used to provide a 1x camshaft signal to the PCM. The PCM uses this camshaft signal to determine intake or exhaust stroke for any given cylinder during engine operation.

Vortec distributor installed in engine.

Written by Mike Noonan and Posted with Permission of CarTechBooks

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GM Gen III LS PCM/ECM: On-Board Diagnostics Troubleshooting

LS Engine DiY — Mon, 16 Feb 2015 01:06:59 +0000

Modern fuel injection systems have many sensors and switches installed at key locations on the engine and transmission to allow the engine (and transmission) computer to operate in the ways they are intended. These sensors and switches are used to deliver the proper amount of fuel, the correct amount of spark timing, the most appropriate transmission gear, and so on. They also provide important information that is valuable for problem diagnosis. The process by which the engine and transmission controller(s) process sensor data and report errors is called on-board diagnostics (OBD). OBD has been used with GM engine controllers since the 1980s. Since that time, OBD has improved to a robust diagnostic system.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

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Assembly Line Diagnostic Link

The OBD system of the first multi-port V-8 electronic fuel injection system, or Tuned Port Injection, was implemented into the 1985 ECM found in the Corvette, Camaro, and Firebird. This basic system uses sensor data to determine if unusual operating behavior exists. When the ECM determines a malfunction, it applies a ground to the service engine soon (SES) lamp in the instrument cluster to indicate the need for service. SAE recommendations have since renamed the SES lamp to the MIL for standardization among vehicle manufacturers.

When the MIL has illuminated, the repair technician must be able to see what the ECM has detected as a malfunction. The malfunction is logged in the ECM as a trouble code. A physical method for retrieving a trouble code is to connect a scan tool to the assembly line diagnostic link (ALDL) connector beneath the dashboard near the steering column. The scan tool displays the trouble code number and the repair technician can then look up the diagnostic procedure to troubleshoot through the problem.

For example, the ECM may log a “Code 33.” The GM service manual diagnostic description informs the repair technician that the MAF sensor signal voltage was too high during an engine operating condition that should not produce such high voltage. In other words, the MAF sensor reported an amount of incoming air that General Motors preconfigured the ECM to determine as improbable for the engine speed and throttle angle at which the trouble code was set.

The GM service manual diagnostic procedure leads the repair technician through a series of tests to determine why this occurred and may point to a faulty MAF sensor. This early OBD system offers a way to flash (illuminate) the MIL to represent the numerically named trouble codes that are set.

OBD-I System

In the 1980s, automotive manufacturers had widely implemented OBD into ECMs. The OBD-I systems were used with annual California emissions testing, but without OBD standardization, the emissions testing program was not as effective as it is today.

The OBD-I diagnostic connector (left) is easily identifiable because it is dimensionally different than the OBD- 1.5 connector (middle) and the OBD-II connector (right), which are dimensionally the same.

OBD-I, OBD-1.5, and OBD-II diagnostic connectors are not wired the same. Provision was made with the OBD-1.5 connector to allow for the OBD-II wiring standard. Compared to the OBD-II connector wiring, the OBD-1.5 adds wires for OBD-I diagnostic test and serial data communication. A look at 1995 GM wiring schematics reveals that the Class 2 serial data wire in connector cavity 2 was not used, but terminated in the dash harness for use in 1996. An OBD-II scan tool is not appropriate for use with an OBD-1.5 vehicle because it cannot read the OBD-I serial data stream.

OBD-1.5 System

The precursor to the standardized OBD-II system was implemented in select 1994 and 1995 GM vehicles. Although not an official name, this OBD system is now referred to as OBD-1.5 because it introduced elements of the OBD-II system. Enthusiasts recognize the 1994–1995 LT1-equipped vehicles as OBD-1.5. This OBD hybrid continues to use some of the same naming conventions as the early OBD systems, but also implements some of the newer OBD-II naming conventions. For example, with OBD-I, a “Code 15” indicates that the ECT sensor signal is too high. With OBD-II, a “P0118” indicates that the ECT sensor signal is too high.

Trouble code retrieval from OBD- 1.5 systems requires a scan tool.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

OBD-II System

In 1996, OBD-II was largely standardized and became a requirement for production automobiles. Benefits include improved diagnostics with many more parameters, ECU programming through the vehicle’s diagnostic connector, and bi-directional control of certain on-board modules.

OBD-II standardization has been an incentive for Manufacturers to offer OBDII scan tools. A brief Internet search reveals hundreds of available OBD-II scan tools. This is Drew Technologies’ DashDAQ-XL, a high-end, feature-packed scan tool. This model has windshield mount (standard), GPS receiver (optional), and bench-top OBD-II power assembly (an EFI Connection product used here as a power source). The DashDAQ-XL touch-screen user interface is used to retrieve and clear DTCs, display both generic and enhanced OBD-II PIDs for monitoring real-time data, and accept aftermarket analog and serial input devices (such as wide-band O2 sensors, thermocouple, and accelerometer). Because of OBD-II standardization, the DashDAQ-XL is compatible with all vehicles since 1996.

OBD-II Data Link Connector

The SAE J1962 OBD-II standard calls for a standardized DLC that is typically located beneath the dashboard and near the steering column. The DLC is used to retrieve DTCs, retrieve real-time data from all networked ECUs, bi-directional diagnostic communication, and ECU programming. For the purposes of Gen III fuel management discussion, the DLC is pinned as follows. Unused connector cavities may be used for vehicle specific functions.

Diagnostic Trouble Code Retrieval

The standardization of OBD-II allows for DTC retrieval with any off-the-shelf OBD-II scanner. DTCs may be present within multiple onboard ECUs and are distinguished by a prefix character followed by four digits. The PCM processes and may set engine- and transmission-related DTCs. Other modules, such as the BCM, are responsible for processing non-powertrain–related DTCs. All off-the-shelf OBD-II scan tools have the capability to retrieve DTCs and clear DTCs from memory. In some cases, and through certain scan tools, freeze-frame data can be retrieved to see operating parameter that occurred when a DTC was set.

For standalone conversions, the DLC for Gen III PCMs requires only serial data, ground, and 12V battery. OBD-II scan tools use the DLC ground and 12V battery for power.

There are several types of OBD-II DTCs. For clarity, DTCs are prefixed by a character that represents the system reporting a fault. Most standalone engine conversions only experience the powertrain (PXXXX) codes, as other systems are typically not present in a conversion vehicle.

An inexpensive, off-the-shelf OBD-II scan tool retrieves only a small set of PIDs. This “generic” PID set displays useful real-time data for troubleshooting the engine and transmission.

Higher-end scan tools display manufacturer-specific PIDs that reveal a more in-depth look at the operation of the engine and transmission. This “enhanced” PID set is more expensive. This cost is often built into the price or available as an add-on feature.

Real-Time Data Monitoring

OBD-II scan tools display real time data by querying (request and response) on-board ECUs. Although scan tool interfaces vary, a repair technician specifies a parameter ID (PID) and the scan tool sends a request through the DLC for that PID (or list of PIDs). The on-board ECU containing that PID responds with the data values for the requested PID. While PIDs are technically codes, scan tools identify PIDs by their representative name, such as “Engine Speed.” Most off-the-shelf scan tools are universal in that they only retrieve the list of PIDs that automobile manufacturers are required to display. The standard, or “generic,” set of PIDs contains useful sensor data about engine and transmission operation. Automobile manufacturers also define their own, non-standard, set of PIDs. These “enhanced” or “extended” set of PIDs are proprietary and greater in number than the standard PID set. Many off-the-shelf OBD-II scan tools do not query on-board ECUs for these PIDs. Scan tool manufacturers must pay a significant fee to obtain information about manufacturer-specific PIDs. Because of the extra costs involved, your basic $35 scan tool does not include the enhanced set of PIDs. Some scan tools offer enhanced PIDs for an extra fee.

Bi-Directional Diagnostic Communication

Advanced OBD-II scan tools have the ability to command control of certain engine and transmission functions. Engine bi-directional controls include, but are not limited to, electric fan operation, A/C compressor clutch operation, manual control of spark advance, commanded idle control, target air/fuel ratio, and injector performance tests. Transmission bi-directional controls include, but are not limited to, torque converter clutch solenoid control and commanded shift solenoids.

A scan tool package such as EFILive displays generic, enhanced, and user-defined PIDs. EFILive’s hardware interface allows for external signal inputs that can be configured within the software to monitor devices such as a wide-band O2S.

Troubleshooting transmission performance is made easier with EFILive’s bi-directional control of the 4L60-E and 4L80-E transmissions. When bi-directional control is active, you can override PCM control of the transmission functions.

Some advanced OBD-II scan tools are capable of performing a crank angle sensor error (CASE) learn procedure (commonly referred to as “crank learn”). The GM service manual explains that due to tolerances in manufacturing, proper misfire detection requires the engine computer to learn the variances in the relationship of the CKP sensor and the crankshaft reluctor wheel. This crank learn procedure should be performed after installing a new engine computer, engine timing cover, CKP sensor, or crankshaft reluctor wheel. Should the installation of these new parts not set a P1336 DTC, the engine computer relies on the results of the previous, now incorrect, crank learn data.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

ECU Programming

The DLC is the connection point for any ECU programming interface. In the 1980s, engine computers stored calibration data in a flash PROM that was programmed outside the vehicle. All GM OBD-II ECUs have the convenience of reprogramming without removal from the vehicle. Reprogramming is required for ECU replacement, GM service updates, and custom tuning through aftermarket tuning equipment.

Mail-order tuners offer custom programming services to get your vehicle running well enough to be driven or trailered to a local chassis dyno tuning facility. To get programming access to the engine and/or transmission computer, mail-order tuners use an off-board benchtop programming solution such as EFI Connection’s Professional Series OBD-II modular benchtop programming equipment. (See Chapter 4 for more information about benchtop programming.)

Troubleshooting Diagnostic Trouble Codes

The OBD-II system’s DTC malfunction logging is a fast and convenient way to resolve a problem. With OBD-II being standardized, any offthe- shelf OBD-II scan tool displays a list of DTCs that explain why the MIL is illuminated in the dashboard. Most auto parts stores scan your vehicle for free.

I recall a customer who updated his third-generation Firebird (a TPI car) to the Gen III PCM. He participated in the Hot Rod Power Tour and was well out of reach of his tools and diagnostic equipment.

The MIL illuminated in his dash as the engine began to run poorly. He was able to stop at an auto parts store for a free scan. The scan revealed a misfirerelated DTC for a specific cylinder. He chased the spark plug wire from the distributor cap to the spark plug and found that the spark plug was loose. He tightened the spark plug, the auto parts store cleared the DTCs, and he was back on the Power Tour.

Before You Change That Sensor

In some cases the ECU sees several occurrences of a malfunction before setting a DTC. It is important to think through the problem before simply buying new parts.

As an example, let’s say a DTC has set indicating prolonged high voltage in the bank 1 O2 sensor. If you rush to the auto parts store to buy a new O2 sensor, you may waste your time, as well as about $50.

The 1986–1989 TPI ECM (right) contains a PROM carrier (called a MEMCAL) that is installed inside the ECM case. This MEMCAL adapter (beneath the removed ECM cover) bypasses the PROM soldered to its carrier so that a flash PROM can be removed. This equipment requires the removal of the flash PROM for every update made to the engine calibration. The PROM is then inserted into a programming device (left) for erasing and reprogramming. It is a tedious process that many tuners avoid today, making OBD-I tuning a service no longer offered by many engine tuners.

This is an example of an OBD-II bench-top programming solution. The PCM (top left) receives power and data communication through the switch assembly (middle) and can be reprogrammed with a laptop or desktop through a programming interface cable (right).

First look at what the O2 sensor does. The O2 voltage ranges from about 0 to 1V. When a lean mixture passes the sensor, the voltage is closer to 0V. When a rich mixture passes the sensor, the voltage is closer to 1V. The target voltage for a healthy running engine is about 0.5V. An O2 sensor in good working order indicates too much fuel in the air/fuel mixture exhausting from the engine. Such a DTC would not warrant an O2 sensor replacement, but rather a look at the fuel injectors on bank 1 to inspect for a faulty injector.

Follow the Manufacturer’s Procedures

The GM service manual contains step-by-step diagnostic procedures for each DTC. In some cases, the documentation includes wire schematics to help you understand the electronic circuits involved. The diagnostic procedures may call for a visual inspection, voltage test light, or multimeter to check voltage or resistance values. Advanced diagnostics may call for the use of a GM Tech2 scanner. The Tech2 is a necessity for on-board ECUs other than the engine control module and is seldom used with Gen III electronics conversions.

A good scan tool package, such as EFILive, and a GM service manual go a long way in diagnosing just about any DTC that may set.

Written by Mike Noonan and Posted with Permission of CarTechBooks

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GM Gen III LS PCM/ECM: Wire Harness Selection Guide

LS Engine DiY — Mon, 16 Feb 2015 00:43:38 +0000

As the owner of EFI Connection, engine wire harness manufacturing is my specialty. In the early days of my career, I took on used harness rework for 1985–1992 Camaro and Firebird owners who wanted to add a TPI system to their car. I’ve also revised newer LS harnesses for customers who have relocated components in the engine bay. Today, however, I decline nearly all used harness rework. With few exceptions, I recommend new engine wire harness builds whenever possible.

Used Wire Harnesses

The reality of any used engine wire harness is that it was removed from an old, and likely salvaged, vehicle. These harnesses may have damage due to heat, chaffing, or improper repair. Proceed with caution before reusing an old wire harness for your high-dollar retrofit.

This engine wire harness was pulled from a 1997 Trans Am before an LS1 PCM conversion (see Chapter 15, Project 3, on page 122). Through a transmission swap, ignition controller, and nitrous installation, this engine wire harness has been modified. The longevity of an engine wire harness may decrease depending on the quality of the modifications.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

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“Let sleeping dogs lie.”

You know that old adage. If it works, leave it alone. If you start messing around, things may get ugly. Some engine bays are left untouched except for oil changes and adding washer fluid; other engine bays have additional wiring for car stereo, alarm, nitrous solenoids, fuel pump relay upgrade, electric water pump, and the list goes on. These add-ons require power, ground, and maybe even sensor signals.

Have you seen the uninsulated butt splice in a vehicle’s wire harness? You know, the red, blue, or yellow plastic barrel that has been crimped on each end? Or maybe you’ve seen an uninsulated blue wire tap? Yes, it’s the handiwork of someone who was in a rush to tie into or repair the vehicle’s wire harness.

Hardware store electrical tape (top) is not the same as harness tape (bottom). Engine wire harness repairs should be completed with quality shrink tube and not wrapped in electrical tape. The electrical tape found at local hardware store contains a lot of adhesive and may not hold up well to engine bay heat. Many auto manufacturers use high-quality Tesa harness tape.

Alternations to a vehicle’s harness often create future points of failure. Even the improper handling of a used wire harness from time of removal to your garage floor may have introduced points of failure that may make you wish you had a custom-built new harness for your project

Let me pause here to tell you about a local street rod project. The early Ford pickup was fitted with an LT1 engine and 4L60-E transmission.

The shop that took on the restoration received the project with a used, reworked engine wire harness. Part of the rework service had included the addition of gear select switch wiring to interface with the LT1 PCM and a custom gear indicator panel mounted on the dash.

I was called after the vehicle was finished because the electric fan did not turn on when the A/C system was on. I also found the used gear select switch connectors were damaged and a previous repair attempt involved forcing wire too large into the connector cavity using a terminal not designed to accept such a large wire size.

Had I been involved with this restoration from the start, the vehicle would have had a brand-new wire harness with all necessary provisions for the vehicle. There would have been no need for a mechanic to add the gear select switch and A/C wiring using the wrong type of insulated wire, butt splice connectors, and generic crimp tool.

This restoration project exceeded $100,000 and, sadly, still has a used engine wire harness with surprises yet to be seen under the black electrical tape.

I’ve heard stories of used engine harness reworks where unused sensor connectors were cut and taped, causing a short as the PCM reference voltage circuit made contact with the PCM low-reference circuit. The methods used to rework used wire harnesses often introduce points of failure.

“Beauty is only skin deep, but ugly goes clear to the bone.”

Going back to that LT1 Ford street rod restoration, I found other surprises as I made repairs. The used harness rework was completed with the application of black electrical tape, which oozes adhesive when the wire harness experiences engine bay heat and leaves a sticky residue as it is removed.

As I unwrapped the sticky electrical tape, I found segments of wire spliced and/or crimped to the harness so that the desired length was achieved. Some “professionals” take the completed engine harness that was designed to fit a specific GM application and shorten or lengthen it by splicing wires to fit the layout of another vehicle. It looks pretty all wrapped up in black tape and split loom. The quality of work within? You roll the dice.

“An ounce of prevention is worth a pound of cure.”

Building a plug-and-play wire harness for any production vehicle requires sourcing connectors and related components (associated secondary locks, dress covers, retaining clips, etc.) that are often specific to the vehicle. These items, if serviceable, are often only available in very large quantities. A harness builder would have to purchase the thousands of connectors, secondary locks, and dress covers and then mark up the price of wire harness builds to reflect these costs.

Delphi manufactures most of the connectors found in GM wire harnesses. In most cases, General Motors uses all available secondary locks during connector assembly. Be cautious of aftermarket harness manufacturers who exclude secondary locks for the sake of saving a few bucks.

All production vehicles pass wires through the firewall somehow. Many have a two-part connection at the firewall called a bulkhead connection. This connection passes through power, ground, and other circuits not carrying sensor signal voltage. Sensor circuits passing through the firewall are typically sealed with a grommet and never cut.

A vehicle that is not appropriate for a standalone, street rod type of wire harness is the 1985–1992 Camaro and Firebird. Unfortunately, General Motors merged much of the engine bay wiring together in 1989, making a new plug-and-play harness a bit more involved than a typical new LS conversion engine wire harness build.

When a customer requests an LS-series PCM conversion wire harness for a 1989–1992 Camaro or Firebird, my typical approach is to build a brand-new wire harness segment for the LS-series PCM with added length at the sensor ends.

The customer sends me the original engine bay harness. It is carefully disassembled to remove the TPI ECM-related wiring and then inspected for damage. Rather than splice in repair segment(s) for a damaged circuit, such as a cut ring terminal at the starter, I place a brand-new length of 10-gauge purple wire in the wire harness, which is terminated at the starter and at the bulkhead connector for the firewall.

I remove the original damaged circuit. After the repairs, I set the remaining original engine bay harness on top of the new harness and finish it on a vehicle-specific template.

The end result is an OEM-quality engine harness that would have been built by General Motors had it used the LS-series PCM in that car.

A wire harness shop should have the proper terminals for GM engine harnesses, be tooled up to make proper crimps using production tooling, and apply proper techniques for reworking an original engine harness. You typically do get what you pay for as many side businesses offering only used harness rework have not invested in the proper supplies (TXL wire and replacement terminals) or crimp tooling to provide you with a product that matches the quality of a new engine harness.

This equipment is expensive and, as a result, causes the repair costs and new construction costs to exceed any low-price deal you find on eBay.

New Wire Harnesses

A brand-new custom wire harness (using the same production tooling and quality components as an OEM harness) is always superior to a reworked, used engine harness. Wire lengths are appropriate for your application, connectors are new (not dirty, brittle, or broken), and the wire does not suffer from oxidation due to years of use in temperature and moisture extremes.

A connector may be used for several different applications. Depending on the circuit requirements, a larger or smaller wire size may be required. Connectors accept a variety of wire sizes but require an appropriately sized terminal. This connector accepts two types of terminals. The 18- to 16-gauge Metri-Pack 150 terminals (the two on the left) allow for 18- and 16-gauge wire. The 22- to 20-gauge terminals (the two on the right) allow for 22- and 20-gauge wire. Each of these terminals was designed to be used with two sizes of wire. What makes this possible is the production crimp die that is used to crimp the terminal to the wire. Cheap, inexpensive, wire harnesses are often built with improper terminal sizes and wrong crimp tooling.

The 18-gauge black wire (left) was crimped with a proper production crimp tool and die set. The 18-gauge red wire (right) was crimped with a general repair tool. You can see that, even with the correct general repair tool, the crimp quality of the red wire is poor compared to the crimp on the terminal with black wire.

The 18-gauge black wire (left) was crimped with a proper production crimp tool and die set. The 18-gauge red wire (right) was crimped with a general repair tool. With a tug of the black wire, the terminal remains firmly attached. However,with a tug of the red wire, the terminal separates from the wire. Be cautious of harness builders who are able to sell products for less by using inexpensive, general repair, tooling.

Inexpensive Gen III wire harnesses are often built with inexpensive general repair crimp tools. Delphi offers a line of general repair crimp tools that do not provide the same crimp quality as with pneumatic press and die sets. Kent-Moore issues the same tools (branded Delphi/Rostra/Kent-Moore/ Sargent) to GM service technicians and clearly explains in terminal repair guides that solder is required for all terminations made with hand tooling. Some wire harness manufacturers may boast they use Delphi tooling. Don’t let that fool you into thinking their wire harnesses are properly assembled.

These hand tools represent production tooling for manufacturing Gen III engine wire harnesses. Each crimp tool contains a die set specific to a type of terminal. In some cases, several die sets are required for a family of terminals. For example, Delphi Metri-Pack 150 sealed terminals require three different die sets to cover 22- to 16-gauge wire. These tools use a parallel crimp (not scissor-like) strategy to accomplish the same quality crimp used with production GM harnesses.

This brand-new, plug-and-play Camaro/Firebird engine wire harness was assembled using all proper TXL wire, Delphi connectors/ terminals/seals, and production tooling. Quality wire harness manufacturers are out there, but be sure to ask the right questions about quality before you choose a manufacturer.

The recipe for a quality engine harness is rather simple: Use the same components and production tooling as General Motors did. Only a few harness shops stand out from the rest because of the high cost involved in material and tooling.

Written by Mike Noonan and Posted with Permission of CarTechBooks

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Upgrading to Gen III LS-Series PCM: Cruise Control Guide

LS Engine DiY — Sun, 15 Feb 2015 17:09:43 +0000

All Gen III vehicles were available with cruise control. Engines with a cable-actuated throttle body require an electronic cruise control module with an internal stepper motor to pull and release a throttle cable to maintain vehicle speed. Engines with an electronic throttle body rely on the TAC module to increase and decrease throttle blade angle to maintain vehicle speed.

Cable Throttle Systems

Early cruise control systems took control of the throttle blade angle through a vacuum-operated actuator that pulled and released a throttle cable. The actuator relied on engine vacuum for operation. Early cruise control systems have a lag response to driver commands. Making cruise control performance worse is an aged diaphragm that has developed a leak and no longer operates properly.

Electronic throttle systems use a TAC module (right), while cable throttle systems use a cable-driven cruise control module (left). The TAC module is wired to a motor mounted within the throttle body assembly and uses PCM data to change throttle angle to maintain cruise control vehicle speed. The cable throttle cruise control module shown here also uses PCM data to maintain cruise control vehicle speed, but must manually pull the throttle linkage to change the throttle angle.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://www.lsenginediy.com/upgrading-gen-iii-ls-series-pcm-cruise-control-guide/

Newer cruise control systems abandoned the vacuum actuator for an electronic module with an internal stepper motor to pull and release a throttle cable to maintain vehicle speed. These systems have a better performance feel than the old vacuum-type systems. The required components of the cruise control system, however, have not changed much.

Required Components

To install a GM cruise control module for your cable throttle system, several components are required. Most of them, such as cruise control switches, clutch switch, and brake switches, may already be in your car. Any missing components can either be sourced from a salvaged GM vehicle or through the aftermarket.

Cruise Control Module: The cruise control module for cable throttle vehicles is a relevant discussion for Gen III PCMs because of the PCM’s availability of primary and secondary VSS outputs that may be used to satisfy the cruise control module’s 4,000 pulse-per-mile input requirement. Also, the 1999–2002 Camaro/ Firebird cruise control modules require cruise inhibit and cruise-enabled status communication signals with the PCM .

Early GM systems used a vacuum-controlled actuator to pull a throttle cable. These systems require a VSS (most commonly a 2,000 pulse-per-mile signal) to maintain cruise control vehicle speed. Rather than using an internal motor like the newer cable-driven cruise control modules, these early units use engine vacuum to control a diaphragm that pulls a throttle cable. The result is a lazy response to the driver’s cruise control commands.

This 1996-newer GM cruise module assembly contains a circuit board for processing cruise control logic, an internal motor to operate a worm-driven gear, and a short braided strap to pull the throttle cable. This cruise control module uses PCM data to control the movement of the throttle cable when cruise control is active.

This Rostra cruise control switch (# 250-3020) may be used in a GM application for on/off and set/coast signals. The aftermarket offers several types of cruise control switches for different steering column configurations. If you cannot identify one to suit your application, you could make your own set of dash or center console-mounted switches. With an on/off switch, two momentary switches, and little creativity, you can create an inexpensive cruise control switch solution.

Cruise control modules compatible with Gen III conversions are plentiful. You may choose from cruise control modules found in 1996- newer Vortec trucks and LS series vehicles. The cruise control module receives signals from several switches and, when necessary, takes control of throttle blade angle through a cable attached to the engine’s throttle body. Installation is rather simple. The most difficult part may be adapting the cruise control throttle cable to your throttle body’s linkage if the cable end does not match.

PCM: In production vehicles, the PCM is used to output a 4,000 pulse-per-mile VSS signal to the cruise control module. This is a common pulse count used with many early GM ECMs and VSS buffer boxes. An optional cruise-engaged status signal is available for communication between the PCM and cruise control module. For retrofits using a 1999–2002 Camaro/Firebird cruise control module, the cruise engaged status and cruise inhibit signal wires must be used.

VSS Signal: The 4,000 pulse-per-mile VSS input to the cruise control module is required, but the PCM is not required to provide it. Retrofit projects sometimes introduce VSS buffer modules to receive a VSS signal that is not compatible with the Gen III PCM and to provide several VSS outputs for devices such as the speedometer or PCM.

Not all aftermarket cruise control switches provide the signals required by the GM systems. This Rostra switch does not provide an independently pulsed 12V signal fo the resume/accel function. In such cases, only the on/off and set/coast switches may be used.

1996-newer GM cruise control module schematic looks like this. Notice the PCM cruise status and cruise inhibit signals are only required for 1999–2002 Camaro and Firebird cruise control modules. In general, the cruise control module requires 12V switched ignition, ground, VSS, cruise control switches, normally open brake switch (stop lamp switch), normally closed brake switch (commonly a torque converter clutch switch), and a manual transmission clutch switch (if so equipped).

This schematic represents a typical GM cruise control switch wired to a TAC module. The TAC module generally requires 12V switched ignition, ground, PCM serial data circuits, cruise control switches, normally open brake switch (stop lamp switch), normally closed brake switch (commonly a torque converter clutch switch), and a manual transmission clutch switch (if so equipped).

A VSS buffer module may also be used to provide a 4,000 pulse-per-mile VSS signal to the cruise control module. Remember, however, the Gen III PCM has two configurable VSS outputs to choose from that provide a 4,000-pulse-per-mile signal dedicated to the cruise control module. (See Chapter 15, Project 1, on page 112 for setting the 4,000 pulse-per-mile VSS signal with EFILive.)

Cruise Control Switches: The required cruise control switch signals the multifunction lever of GM steering columns. The on/off signal is normally open switched 12V, the set/ coast signal is momentary 12V, and the resume/accel signal is momentary 12V.

Rostra Precision Controls offers a variety of cruise control switches that may be used if your steering column’s multifunction lever does not have the necessary cruise control switches. (See Chapter 15, Project 1, on page 112 to see an early GM steering column with only a set/coast cruise control switch.)

Brake Switch: The cruise control module requires two brake switch signals. A normally closed 12V switch applies power to the clutch/brake switch input (pin D) and a normally open 12V switch applies stop lamp voltage to the brake input (pin G). These signals are used to disengage cruise control when the brake pedal is depressed.

Clutch Switch: If using a manual transmission, a normally closed clutch switch should be wired on the same circuit as the normally closed brake switch. Depressing the clutch switch removes 12V from the cruise control module (pin D) to disengage cruise control.

Operation Overview

With the exception of the 1999– 2002 Camaro/Firebird cruise control modules, the 1996-newer truck and 1998 Camaro/Firebird cruise control modules can be used as standalone units. These modules require 12V ignition, ground, cruise control switch signals, brake switch signal, clutch switch signal, stop lamp switch signal, and a 4,000pulse-per-mile vehicle speed signal. Once installed in a retrofit vehicle, the performance is improved compared to early cruise control systems operated by engine vacuum.

Set/Coast: To set cruise control, the cruise control module requires a 12V switched-on signal and a 12V momentary set signal from the multifunction lever. With the 12V on signal present at the cruise control module and the vehicle at a desired speed, pushing the set button adds the vehicle’s current speed to the cruise control module’s memory.

The driver may remove his or her foot from the accelerator pedal and the cruise control module overrides the throttle blade angle to increase or decrease vehicle speed. Pressing and holding the set/coast button causes the vehicle to coast to a reduced speed. Releasing the set/coast button stores the new reduced vehicle speed in the cruise control module’s memory. Quickly pressing and releasing the set/coast button subtracts 1 mph from the cruise control module’s memory.

Resume/Accelerate: Once cruise control is active and the driver depresses the clutch or brake pedal, the cruise control module no longer controls throttle blade angle. The previously set vehicle speed remains stored in the cruise control module’s memory. Sliding the resume/accel switch requests the cruise control module to take over throttle blade angle and accelerate the vehicle to the previously set vehicle speed.

Sliding and holding the resume/ accel switch increases vehicle speed until the switch is released. The new vehicle speed is stored in the cruise control module’s memory. Quickly sliding and releasing the resume/ accel switch adds 1 mph to the cruise control module’s memory.

If the cruise control on/off switch is set to off or the vehicle is shut off, the cruise control module’s memory is erased and sliding the resume/accel switch does not return the vehicle to a previously set speed.

Erasing Cruise Speed Memory: When the driver disengages cruise control by depressing the clutch or brake pedal, the cruise control module retains its memory and allows the driver to use the resume/accel switch to resume the vehicle speed stored in memory. To clear the cruise control module’s memory of vehicle speed, turn off the on/off switch or shut off the vehicle’s ignition switch. This removes 12V power from the cruise control module and clear its memory.

Disengaging Cruise Control: The cruise control module retains the set vehicle speed in its memory until it loses 12V power through the cruise control on/off switch or the vehicle’s ignition switch. To disengage (but not disable) the cruise control module’s control of throttle blade angle, gently apply the clutch or brake pedal to momentarily remove 12V power from the cruise control module’s brake/clutch signal input.

To disable cruise control, slide the cruise control on/off switch to the off position.

Inhibit Signal

Be cautious of cruise control modules from 1999–2002 Camaros/ Firebirds. These cruise control

modules are “more intelligent” than truck modules. In the 1999–2002 Camaro/Firebird, the PCM may inhibit (prevent) cruise control operation based on vehicle speed, park/neutral switch signal, engine RPM, or battery voltage. If the PCM commands the cruise inhibit signal to the cruise control module and the cruise control module returns an active cruise-engaged status signal, the PCM sets a DTC related to the cruise control system.

Most people find this extra layer of protection unnecessary and prefer a cruise control module from a 1996-newer truck or 1998 Camaro/ Firebird. The 1998 Camaro/Firebird PCM cannot output a cruise inhibit signal, so the 1998 Camaro/Firebird cruise module functions the same as the 1996-newer truck modules.

Identifying a 1999–2002 Camaro/ Firebird cruise control module is rather easy. All ten harness connector cavities are used. Vehicles with the cruise inhibit signal require its use when installing the cruise control module in a retrofit vehicle. While you likely do not see a wire in connector

cavity H for any other vehicle, a quick visual inspection of the wire harness shows whether the cruise inhibit signal is required.

Electronic Throttle Systems

All Gen III vehicles with an electronic throttle body rely on the TAC module for cruise control operation. During normal engine operation, the TAC module is used to increase and decrease the throttle blade angle. By using the available cruise control switch inputs, the TAC module can respond to the driver’s cruise control commands to maintain vehicle speed.

Being fully integrated into the electronic throttle system, the driver’s cruise control commands are instantaneously applied to the throttle and the feel of acceleration and deceleration is smooth and seamless.

The switches and inputs are very similar to those of cable-operated cruise control modules.

Required Components

It’s likely that after an electronic throttle installation your vehicle will have all of the components necessary for integrated cruise control. By using the TAC module’s cruise control switch inputs and brake/clutch switches, any retrofit vehicle can be ready for cruise control. The following switch signals are required by the electronic throttle system for cruise control operation.

Cruise Control Switch: The required cruise control switch signals are no different than those for Gen III vehicles with cable throttle body and cruise control module. The on/ off signal is normally open-switched 12V, the set/coast signal is momentary 12V, and the resume/accel signal is momentary 12V. If your retrofit vehicle does not have a multifunction lever on the steering column with cruise control switches, you can find them in the aftermarket.

Brake Switch: The cruise control system requires two brake switch signals. A normally closed 12V switch applies power to the TCC brake switch input of the PCM and a normally open 12V switch applies stop lamp voltage to the stop lamp input of the TAC module. These signals are used to disengage cruise control when the brake pedal is depressed.

Clutch Switch: If using a manual transmission, a normally closed 12V clutch switch must be wired to the PCM (blue connector, pin 35). Depressing the clutch switch removes 12V from the PCM’s clutch switch input to disengage cruise control.

Written by Mike Noonan and Posted with Permission of CarTechBooks

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Upgrading to Gen III LS-Series PCM: Air Conditioning Guide

LS Engine DiY — Sun, 15 Feb 2015 02:31:07 +0000

All too often PCM-controlled (or monitored) air conditioning is overlooked after the engine has been swapped, the new wire harness has been installed, and custom calibrated PCM has been received from the tuner. The A/C system is commonly one of the many “I’ll think about that later…” tasks as the excitement builds for the first engine startup.

I recall an LS1 engine conversion in an early Corvette that followed this scenario. I discussed the project with the shop owner before building the engine harness so that nothing would be missed. He wanted to keep the wiring “clean” and not have A/C wiring related to the PCM. He neglected to think through the aftermarket A/C system wiring and did not realize, until the car was days from scheduled delivery, that there was no way to turn the electric fans on when the A/C system was on.

Being pressed for time to meet the deadline and out of money to make further changes to the car, he compromised with an undesirable workaround, by turning the fans on at 30 degrees F through the PCM. Now he had a $100,000 Corvette with an electric fan solution that General Motors never would have implemented, even in a $10,000 car!

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

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Base Calibration

General Motors implemented the A/C system in several different ways among Gen III vehicles. The PCM calibration is specific to each of these implementations. Of most importance is the consideration of electric fan control.

If your project uses electric fans, begin with a PCM calibration from a vehicle that has electric fans.

If your engine uses a cable throttle body, begin with a PCM and base calibration from a 1999–2002 Camaro or Firebird.

If your engine uses an electronic throttle body, begin with a PCM and base calibration from a 1999–2002 Corvette. (See Chapter 8 for more about Corvette electronic throttle equipment.)

If your project uses electric fans and the PCM and calibration is based on a truck, the PCM does not turn on the electric fans when the A/C is on. Truck PCMs older than 2003 can be reflashed with 1999–2002 Camaro, Firebird, or Corvette calibrations for proper electric fan operations.

Operation Overview

In the 1990s, General Motors introduced PCM control of the A/C compressor clutch. While the operation of the A/C system hasn’t changed significantly, there’s been a few improvements. Fuel injection enthusiasts should consider several things such as the diagnostic feedback, functional benefits, and safety of PCM-controlled A/C.

The Gen III PCM supports DTC processing for the A/C system. The DTCs shown here may be enabled to report a fault in the A/C pressure sensor or A/C compressor clutch (or related wiring). Notification of a fault is presented to the driver through the MIL or a scan of the OBD-II diagnostic port.

EFILive tuning software presents calibration details for the operation of the A/C compressor clutch. Notice that the A/C compressor is disabled above 4,895 rpm or a TPS value of 100 percent (also known as WOT).

In a production GM application where electric fans are used and the A/C is on, the PCM commands the Fan #1 control circuit on (which is actually going to turn on both fans at low speed; see Chapter 10) through calibration {G0903} Fan #1 Turn-on By A/C Temp. With the electric fans on above the specified coolant temperature, the PCM monitors the A/C pressure signal and uses calibration {G0911} Fan #1 A/C Pressure Enable to allow electric fan operation, and calibration {G0912} Fan #1 A/C Pressure Disable to prohibit electric fan operation.

OBD-II diagnostics can be helpful in troubleshooting your vehicle’ A/C system. With a handful of A/C related DTCs, the first step in identifying a problem may be a quick look through the OBD-II diagnostic port at DTCs that have been set. A brief description of a logged DTC malfunction may point you directly to the source of the problem. Depending on your PCM’s calibration settings, your scan tool may display very useful information about A/C faults.

It is not always appropriate to engage the A/C compressor clutch when the driver commands the A/C compressor to turn on. The PCM monitors the pressure of the A/C system to determine if the A/C compressor clutch should engage with the driver’s turn of the A/C control knob. More than that, the PCM also considers other engine operating data such as RPM, throttle position, and intake air temperature.

To prevent damage to the A/C system, it is crucial that air passes through the A/C condenser when the A/C compressor clutch is engaged. Because the PCM controls the operation of the electric fan(s), it is capable of turning on the fan(s) when the A/C is on to pass air through the A/C condenser. The PCM applies coolant temperature and A/C pressure logic to the operation of the electric fan(s).

Request Input

A 12V signal wire is monitored at pin 17 of the red PCM connector. With no voltage applied, the circuit is open and the PCM does not attempt to turn on the A/C compressor clutch. When 12V is applied to the circuit and based on the pressure in the system, the PCM commands the A/C compressor to turn on.

Pressure Sensor

Common among Camaros, Firebirds, and Corvettes, the A/C pressure sensor provides a 0 to 5V signal to pin 14 of the red PCM connector. Based on this signal, the PCM does or does not command the A/C compressor to turn on when the driver requests A/C operation. A common location for the A/C pressure sensor is the passenger’s side of the engine compartment ahead of the A/C accumulator/drier.

This sensor is in a 1997 Trans Am. In this vehicle, the LT1 PCM also uses the same 0 to 5V A/C pressure signal as part of the logic that determines whether the A/C compressor clutch is engaged.

Low-Pressure Switch

Common among trucks and vans, the A/C low-pressure switch is used as an input to the PCM (up to 2002) or HVAC control module (2003-newer) as part of the logic that determines whether the A/C compressor clutch is engaged. This switch provides a ground signal to the PCM or HVAC control module when the A/C pressure is not low. When the A/C pressure is low, the circuit is open and the A/C does not turn on.

When the driver turns on the A/C system and the PCM determines the system is ready for A/C operation, the PCM activates the A/C compressor clutch relay. If the relay does not supply 12V to the A/C compressor clutch, then the PCM sets DTC P1546. This indicates a problem with the A/C compressor clutch relay or related wiring.

This switch is in a 2003 Silverado A/C accumulator/drier. Be sure to check the wiring schematics for the vehicle type your PCM calibration is based on because this switch is not used with all LS-series vehicles.

Clutch Relay

When the driver commands the A/C on from the control unit and the system pressure criteria is met, the PCM grounds the A/C compressor clutch relay coil to turn on the A/C. This relay is most often found within a fuse block assembly.

In the 1997 Trans Am, General Motors located the A/C compressor clutch relay within the fuse and relay box in the front driver’s side of the engine bay.

On Input

As a secondary check, the PCM looks for A/C compressor clutch voltage on pin 18 of the red PCM connector. If the PCM has commanded the A/C on and 12V is not found on this input, the PCM sets DTC P1546 to indicate that the circuit is unexpectedly open. A likely cause for this DTC is a faulty A/C compressor clutch relay.

Compressor Clutch Solenoid

Located within the A/C compressor, this solenoid is responsible for engaging the A/C compressor clutch. A diode is installed either in the wire harness or within a fuse block assembly to block a high-voltage spike as the A/C compressor is cycled on and off.

While there is a variety of A/C compressors, they all use a solenoid to engage the compressor clutch to pressurize the system. This A/C compressor is included with the Chevrolet Performance small- and big-block Chevy front accessory drive kits. Notice the wire harness connection for the clutch solenoid at the top of the compressor just behind the pulley.

Electric Fan Wiring

For proper electric fan control when the A/C is on, the best PCM and calibration choice is 1999–2002 Camaro/Firebird/Corvette. In these vehicles, the PCM receives a 12V request from the control head, checks the refrigerant pressure, activates the compressor clutch relay, and monitors the voltage on the compressor clutch to verify that the compressor has been turned on.

Because the A/C compressor cycles on and off, a diode is found in GM wire harnesses to block a high-voltage spike. This diode is sometimes found within a fuse block assembly

When the A/C system is on, the PCM activates low-speed electric fan operation for series/parallel operation. It turns on only the electric fan 1 relay for on/off operation. (See Chapter 9 for electric fan schematics.)

Eliminating the Pressure Sensor

The A/C pressure sensor can be difficult to install in early vehicles because there may be no provision for it. An alternative to using this pressure sensor is to fake the refrigerant pressure signal by replacing the sensor with an 80,000-ohm, 1/4-watt resistor. The resistor can be installed between the 5V reference (pin 45, blue PCM connector) and signal (pin 14, red PCM connector). The compressor clutch engages regardless of refrigerant pressure.

An alternate method of logic should be applied to the 12V A/C Request Signal on pin 17 of the red PCM connector. Install some type of safety pressure switch(es) between the A/C control head and the PCM. An existing or aftermarket system may already include logic to the 12V A/C compressor clutch supply circuit. This circuit can be used to supply the 12V A/C request signal on pin 17 of the red PCM connector.

Compressor Clutch Control

Early LS-series trucks and 2001– 2002 vans were not equipped with electric fans. These vehicles use one or more switches as part of the logic that determines if the compressor clutch should turn on when the driver commands the A/C on through the control head. This system does not use the 0 to 5V pressure sensor found in the Camaro, Firebird, and Corvette.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://www.lsenginediy.com/upgrading-gen-iii-ls-series-pcm-air-conditioning-guide/

When using electric fans, it is best to choose a PCM and calibration from a 1999–2002 Camaro, Firebird, or Corvette. General Motors fitted these vehicles with electric fans and made a provision within the PCM for A/C operation that relies on the use of the electric fans for keeping the condenser cool. This wiring schematic represents the A/C system in the 1999–2002 Camaro, Firebird, and Corvette.

For vehicle installations where the A/C pressure sensor cannot be installed, the voltage necessary to indicate proper line pressure can be created through the installation of a resistor. By installing an 80,000- ohm, 1/4 watt resistor across the A/C pressure sensor, 5V reference, and signal circuits, the PCM thinks the A/C pressure is always adequate for A/C compressor clutch operation. This workaround should be used with extreme caution as it eliminates the safeguards General Motors has implemented through the use of an A/C pressure sensor.

The A/C system wiring for the 1999– 2002 trucks and vans is represented here. This system does not use the 0 to 5V A/C pressure sensor found in the Camaro, Firebird, and Corvette. These trucks and vans were not fitted with electric fans. If you plan to use electric fans, consider using the wiring and PCM calibration from a 1999–2002 Camaro, Firebird, or Corvette

In 2003, General Motors introduced HVAC control modules in trucks and vans that replaced the traditional 12V A/C on signal with Class 2 serial data messaging. For conversions requiring a 2003-newer Gen III PCM, the A/C system has to be wired independent of the PCM.

There are variations on the implementation of this A/C system, so refer to the GM schematics when necessary.

A benefit of implementing this wiring in your non-electric fan project is that you can make use of

PCM control of the A/C compressor clutch based on engine RPM, throttle position, and so on.

A big problem with PCM controlled A/C was introduced in 2003. In an effort to reduce the amount of wire in newer automobiles, serial communication lines were established for modules to communicate across the vehicle. Most 2003-newer PCMs receive Class 2 serial data messaging from the HVAC control module. The early 12V A/C request from the A/C control unit is no longer used and has not been used in a GM vehicle since.

LS PCM conversions using the 2003-and-newer PCMs must disable the DTCs related to A/C and not

bother with wiring in the A/C pressure sensor. If the vehicle is equipped with electric fan(s), they must be turned on when the compressor clutch is engaged. A trigger wire from the A/C wiring must be wired into the electric fan relay(s) to pass air through the condenser when the A/C is on. If the PCM has not commanded the electric fan(s) on based on high coolant temperature and a ground is applied to the fan relay signal wire(s), DTC(s) set to indicate that the fan(s) have been turned on unexpectedly. The DTC(s) can be disabled through tuning software.

PCM Conversion Recommendations

For LS PCM conversions with cable throttle, the most desirable PCM and base calibration is the 1999– 2002 Camaro/Firebird. Those calibrations support A/C compressor control and electric fan control. The Camaro/ Firebird calibrations allow you to choose between manual transmission and 4L60-E automatic transmission. Should your LS PCM project require control of a 4L80-E transmission, a segment swap does the trick. Not all tuning software packages allow segment swaps but those that do, such as EFILive, provide necessary details.

The A/C pressure sensor (left) reports a 0 to 5V signal to pin 14 of the red PCM connector that represents the pressure of the A/C system. The A/C low-pressure switch (right) indicates whether the A/C pressure is low by applying a ground to pin 55 of the red PCM connector.

For LS PCM conversions with Corvette electronic throttle equipment, a Corvette base PCM calibration must be used. The Corvette calibrations allow you to choose between manual transmission and 4L60-E automatic transmission. Should your LS PCM project require control of a 4L80-E transmission, a segment swap does the trick.

For LS PCM conversions with truck electronic throttle equipment, the corresponding truck PCM and base calibration must be used. The early truck calibrations support A/C control, but not electric fan control. The 2003-newer truck calibrations do not support A/C control without the enormous task of integrating the HVAC control module for Class 2 communications with the PCM. For these types of LS PCM conversions, when the A/C system is on, electric fan operation has to be implemented without control from the PCM.

Written by Mike Noonan and Posted with Permission of CarTechBooks

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If you liked this article, you will LOVE the full book!
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The post Upgrading to Gen III LS-Series PCM: Air Conditioning Guide appeared first on LS Engine DIY.

Upgrading to Gen III LS-Series PCM: Transmission Guide

LS Engine DiY — Sun, 15 Feb 2015 02:04:49 +0000

Gen III PCM control goes beyond the engine to be one of best solutions for electronically controlled 4-speed automatic transmissions. Owners not using the LS1 PCM for engine control must look to the aftermarket for a standalone transmission controller that may cost in excess of $1,000. While many who desire an automatic transmission choose either a 4L60-E or 4L80-E transmission when using the LS-series PCM, others may simply disregard the PCM’s transmission functions and use a non-electronically controlled automatic or manual transmission.

Automatic Transmissions

In general, any automatic transmission can be used in a vehicle where the engine is controlled by a Gen III PCM. For early transmissions, the aftermarket offers simple solutions for an electronic vehicle speed signal and standalone torque converter lockup. Most late-model, electronically controlled transmissions can be fully controlled with the LSseries PCM. For electronically controlled transmissions not compatible with the LS-series PCMs (1993–1995 4L60-E transmissions), the aftermarket offers standalone transmission controllers.

The aftermarket has a variety of vehicle speed sensors available for transmissions that use a speedometer cable. This Painless Wiring VSS (# 60116) installs between the transmission and speedometer cable to output an electronic vehicle speed signal that can be used by Gen III PCMs.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://www.lsenginediy.com/upgrading-gen-iii-ls-series-pcm-transmission-guide/

Regardless of automatic transmission choice, tuners usually begin with an LS-series calibration from an automatic transmission vehicle to retain proper engine idle characteristics.

It is wise to consult a professional transmission builder for actual fitment details. With the wide variety of engines, transmissions, flexplates, and torque converters, a mismatch of components can easily be avoided with help from someone with experience.

Non-Electronic Control

Transmissions with no electronic control should be fitted with a VSS to satisfy the PCM’s vehicle speed input requirement. Although early transmissions are typically equipped to accept a mechanical speedometer cable, the aftermarket offers electronic VSS adapters that continue to allow the use of the speedometer cable while satisfying the PCM’s VSS input.

Electronic Torque Converter Lockup

The electronic torque converter lockup function for non-electronically shifted transmissions (200-4R and 700-R4) is not compatible with the Gen III PCMs. These transmissions use an ON/OFF solenoid to apply torque converter lockup while the LS-series PCMs provide PWM control to a torque converter lockup solenoid. Fortunately, the aftermarket offers standalone torque converter lockup kits for applications where the ECM/PCM cannot control torque converter lockup.

This B&M torque converter lockup kit (# 70248) allows for torque converter lockup operation for 200-4R and 700-R4/4L60 transmissions. It is not for use with 4L60-E, 4L80-E, or any other electronically controlled automatic transmission.

1993–1994 4L60-E Transmissions

The 1993–1994 4L60-E transmissions are not compatible with Gen III PCMs. General Motors introduced the 4L60-E transmission in 1993. In design, this transmission is unique in that the PCM is used to control shift solenoids. Drivability is a seat-of-the pants noticeable improvement compared to the 700-R4; the 700-R4 shifts through the gears by means of a detent cable attached to the throttle linkage and weights and springs in the governor. These early 4L60-E transmissions do not have a TCC PWM solenoid, which was added to the 4L60-E transmission in 1995 to assist in applying torque converter lockup.

1995 4L60-E Transmission

The 1995 4L60-E transmission is not compatible with the Gen III PCM. In 1995, General Motors added a TCC PWM solenoid that was used in combination with the TCC lockup solenoid to assist in smoothly applying torque converter lockup. This update is visually noticeable in the 1995 wire harness as a brown wire that was added to connector cavity U of the 4L60-E harness connector.

1996-Newer 4L60-E Transmissions

The 1996-newer 4L60-E transmissions are compatible with Gen III PCMs. In fact, they are compatible with 1996-newer GM PCMs. In 1996, General Motors changed the operation of the 3-2 downshift solenoid from PWM to ON/OFF operation through a ground path provided by the PCM. The 1995 and 1996 wire harnesses are identical, using 13 cavities of the transmission harness connector.

Other compatible 4L60-E type transmissions include the 4L65-E and 4L70-E. But don’t let the 4L65-E name fool you; this transmission is electronically equivalent to the 4L60-E transmission, receiving little more than one additional planetary gear (five gears total) and several stronger internals for improved strength. The 4L70-E is used with Gen IV ECM/TCM systems and can be found in the Chevrolet Trailblazer. This transmission adds an ISS but it is electronically compatible with Gen III PCMs. Very simply, the ISS output signal is not used (or required) by Gen III PCMs.

4L80-E Transmissions

Enthusiasts requiring a stronger, electronically controlled automatic transmission may consider the 4L80-E transmission. These were installed in many 2500-series GM trucks and can be controlled with Gen III PCMs. The 4L60-E and 4L80-E transmissions use the same harness connector, but are wired a little differently. Tuners must use either a calibration from a truck that has a 4L80-E or perform a transmission segment swap within the PCM calibration.

6L80 and 6L90 Transmissions

General Motors introduced 6-speed automatic transmissions in certain 2006 performance vehicles (Corvette and Pontiac G8). These transmissions feature a built-in TCM identified as a T43 TCM. It communicates with the ECM through CAN messaging. Without the proper CAN messaging (to and from a Gen IV ECM), these transmissions cannot be used.

At the time of this writing, the aftermarket has not made a standalone controller available for the 6L80 and 6L90 transmissions. With no CAN support, the Gen III PCM cannot be used to control the T43 TCM.

The 6L80 and 6L90 (shown) transmissions are used with Gen IV vehicles. These transmissions require a TCM mounted internally on the valve body. These T43 TCMs require CAN bus communication with a Gen IV ECM for operation. The 6L80 and 6L90 transmissions cannot be used in a Gen III PCM conversion.

Manual Transmissions

In general, any manual transmission can be used in a vehicle where the engine is controlled by a Gen III PCM. Regardless of manual transmission choice, tuners usually begin with an LS-series calibration from a manual transmission vehicle. It is wise to consult a professional transmission builder for actual fitment details. With the wide variety of engines, transmissions, flywheels, and clutches, a mismatch of components can easily be avoided with help from someone with experience.

The 1999–2002 PCM has been used in the Camaro and Firebird to control two T56 manual transmission functions: skip shift and reverse lockout. The PCM may also receive an input from the CPP switch. These functions are optional and most owners choose to eliminate skip shift.

The skip shift function is controlled by the PCM through a solenoid mounted on the transmission. During certain operating conditions, the PCM requires the driver to shift from first to fourth gear, preventing the driver from shifting into second or third gear. Skip shift settings can be changed within the PCM’s calibration.

EFILive presents several settings for computer aided ratio select (CARS) or computer aided gear select (CAGS). Used with T56 manual calibrations only, this feature locks the driver out of second and third gear during city-like driving conditions. Most owners choose to disable this feature.

C.A.T.S OBD-II tuner software presents settings for the reverse lockout feature used with T56 manual transmission calibrations. This feature assists the driver by making it difficult to enter reverse gear while the vehicle is in motion.

Corvettes and GM trucks use a 12V CPP signal; Camaro and Firebirds use a ground CPP signal. The type of CPP signal is set within the PCM calibration, but requires an advanced tuner to make the change.

The reverse lockout function is controlled by the PCM through a solenoid mounted on the transmission. When the solenoid is energized, the driver can easily shift the transmission into reverse. The PCM allows reverse gear whenever vehicle speed is below 5 mph and prevents the driver from shifting the transmission into reverse above 5 mph. Reverse lockout settings can be changed within the PCM’s calibration.

When loaded with a manual transmission calibration, the PCM expects a signal from a CPP switch. GM trucks and Corvette are set to receive a 12V signal (normally closed). The Camaro and Firebird are set to receive a ground signal (normally closed) to indicate clutch pedal status. This circuit is not used to prohibit the engine from starting; it is used for cruise control function and engine control during shift transitions.

Written by Mike Noonan and Posted with Permission of CarTechBooks

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The post Upgrading to Gen III LS-Series PCM: Transmission Guide appeared first on LS Engine DIY.

Upgrading to Gen III LS-Series PCM: Electric Fan Guide

LS Engine DiY — Sun, 15 Feb 2015 01:38:10 +0000

Gen III PCMs are powerful control modules but they are of little use without tuning software to change engine (and transmission) operating parameters.

Before getting too far into a discussion of electric fans and PCM calibrations, it is important to first consider air conditioning control.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

Air Conditioning Considerations

Prior to buying a custom wire harness or doing PCM calibration work, determine if the vehicle will have air conditioning, if electric fan(s) are required when the A/C compressor is on, and if the PCM will be used to control the electric fan(s). (See Chapter 12 for more detail.)

Will the Vehicle Have Air Conditioning?

If the vehicle is fitted with air conditioning, the engine experiences additional load when the A/C compressor clutch is engaged (A/C is on). For engine retrofits, many PCMs (excluding 2003- newer) have an A/C on input that allows the PCM to adjust for the additional engine load, avoiding low-RPM stumble. Wired properly, and if using an LS1 Camaro, Firebird, or Corvette PCM calibration, the electric fan(s) turn on when the A/C is on to pull air through the A/C condenser.

Will the Electric Fan(s) be Required when the A/C Compressor is On?

When the A/C system is turned on, low-pressure refrigerant gases are drawn into the A/C compressor and transferred to the A/C condenser (located in front of the engine radiator) as high-pressure gas. The A/C condenser is essentially a radiator that cools the high-pressure refrigerant gases into a liquid again, in order to cool the interior of the car. To cool the A/C condenser, air must pass through it. One method of cooling the condenser is to install a permanent mechanical fan in front of the engine (as on many GM trucks). A more common method of drawing air through the condenser (and engine radiator) is through electric fan(s).

Will the PCM be Required to Controlthe Electric Fan(s)?

Many owners operate electric fan(s) independently of the PCM by triggering a relay through either the A/C compressor clutch circuit or through a trinary pressure switch. One drawback to these methods when using Gen III PCMs is that unwanted DTCs set as the PCM detects the fan(s) have turned on during conditions that the PCM has determined the fan(s) should be off. One solution is to simply disable these DTCs, which also disables the intended function of the DTC processing. A better solution is to use the PCM’s A/C control functions to gain improved A/C system control and A/C system diagnostics. (See Chapter 11 for more about A/C control.)

PCM Calibration

Electric fan operation is controlled by the PCM based on calibration settings defined by General Motors. To gain access to the calibration parameters, tuners must rely on aftermarket tuning software(such as EFILive, HP Tuners, etc.) to expose the electric fan settings and make desired changes. Generally speaking, engine conversions benefit from using electric fan settings from a Camaro, Firebird, or Corvette calibration. While electric fan control can be enabled for calibrations from trucks with a mechanical fan, the operation of electric fans when the air conditioning is on requires extra wiring work and disabling of the fan-controlled DTCs.

Many GM trucks equipped with a Gen III PCM use a mechanical fan. They use the typical high-speed-fan control output (red PCM connector, pin 33) as A/C automatic recirculation. When using a PCM with truck calibration, change calibration {G0106} from Auto Recirculation to Fan #2 Control.

GM vehicles equipped with an LSseries PCM and electric fans operate both fans in low-speed and high-speed mode only. This requires two PCM outputs and three relays. By using the two PCM outputs and only two relays, two electric fans can be controlled independently.

GM vehicles equipped with an LS-series PCM and electric fans operate both fans in low-speed and high-speed mode only. This requires two PCM outputs and three relays. By using the two PCM outputs and three relays, two electric fans can be controlled in low-speed and high-speed modes.

Camaro, Firebird and Corvette

The LS1 Camaro and Firebird are fitted with two electric fans and manual A/C controls. The PCM is responsible for controlling both A/C operation and electric fan operation. When the A/C controls are turned on, the PCM receives a 12V on signal, and validates A/C operation through a pressure sensor and 12V A/C compressor clutch status circuit. When the PCM is satisfied that the A/C is truly on, the PCM activates low-speed electric fan operation (for series/ parallel operation), or only turns on electric fan 1 relay (on/off operation).

Because the Camaro and Firebird were only available with a cable throttle body, PCMs loaded with the LS1 Camaro or Firebird calibration are the best choice for cable throttle engine retrofits where the PCM controls both A/C and electric fans.

The LS1 Corvette was available with either automatic or manual A/C controls. Those fitted with automatic A/C controls use a Class 2 data signal from the A/C controls to the PCM to indicate A/C control status. A PCM loaded with a Corvette calibration using automatic A/C controls does not provide the necessary A/C on signal to the PCM for electric fan operation. Owners using Corvette electronic throttle equipment on their engine retrofit should use a PCM calibration from a Corvette with manual A/C controls to satisfy the PCMs A/C on input for electric fan control.

Trucks

GM trucks were fitted with a mechanical fan until 2005 so those PCM calibrations do not have provision for electric fan control with A/C on. In 2005, when electric fans were introduced in GM trucks, both manual and automatic A/C controls communicated with the PCM using the Class 2 data stream, a signal not available in early retrofit vehicles. The best solution for retrofits using the PCM for electric fan control is a 1999–2002 Camaro, Firebird, or Corvette calibration.

PCM Operation

All Gen III PCMs are capable of controlling one or two electric fans.

On/Off

Production vehicles operate two fans with low- and high-speed capability using three relays to switch between series and parallel operation. However, since the PCM is only applying a ground to each fan relay signal circuit, two fans can be controlled through two relays for on/ off operation. In this way the electric fans are always wired in parallel so that each fan receives system voltage.

PCMs with a truck calibration, depending on the year, require the fan outputs to be turned on and on/ off temperatures to be set.

Low/High Speed

Production vehicles operate two fans with low- and high-speed capability by using three relays to switch between series and parallel operation. The third relay is responsible for switching from series (low-speed) to parallel (high-speed) operation.

When the PCM triggers only the low-speed fan output, current flows through both electric fan motors. In this way the electric fan motors are wired in a series and voltage is reduced, causing the fan motors to spin at low speed.

When the PCM triggers the two additional relays, the same voltage flows through each electric fan motor. In this way the electric fan motors are wired in parallel, causing the fan motors to spin at high speed.

Written by Mike Noonan and Posted with Permission of CarTechBooks

LEARN MORE ABOUT THIS BOOK

If you liked this article, you will LOVE the full book!
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The post Upgrading to Gen III LS-Series PCM: Electric Fan Guide appeared first on LS Engine DIY.

GM Gen III LS PCM/ECM: Electronic Throttle Equipment Guide

LS Engine DiY — Sun, 15 Feb 2015 01:08:29 +0000

General Motors introduced electronic throttle, or drive-by-wire, with the LS1 engine in the 1997 Corvette. Electronic throttle was released before cable throttle for the LS-series engine family. In 1998, the Camaro and Firebird received a cable throttle LS1 engine. The GM trucks received LSseries engines in 1999 and, depending on make/model, were available with either cable throttle or electronic throttle. Navigating through the various electronic throttle equipment may be intimidating, but look carefully at the components to ensure success.

1997–2004 Corvette

The Corvette received the same electronic throttle equipment from 1997–2004. Other than a few GM part number updates, the equipment remained the same and electronic throttle equipment can be interchanged. The LS1 and LS6 engines received the same equipment. Everything changed (throttle body, pedal assembly, and TAC) when the LS2 engine was introduced in 2005.

With so many different throttle bodies, pedals, and TAC modules, you must take caution to choose the correct combination of components. Choosing the wrong components could result in no throttle response and an illuminated MIL lamp.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

Throttle Body

The Corvette throttle body is fitted with a TPS to monitor throttle blade angle. It is also fitted with a motor, operated by the TAC module, to open and close the throttle blade. The TPS housing contains two individual sensors with separate signals, low reference, and 5V circuits. The two TPS signals are monitored by the TAC module. As the throttle blade is opened, TPS sensor 1 voltage sweeps toward 5V reference, and TPS sensor 2 voltage sweeps toward low reference. These opposing signals are used by the PCM to monitor and make one throttle angle PID available.

This wiring diagram represents the 1997–2004 Corvette electronic throttle control system.

LS2/LS3 Throttle Body: The 2005–2008 LS2/LS3 throttle body is a popular upgrade for the 1997–2004 LS1/ LS6 Corvette because it is electronically compatible with the 1997–2004 Corvette throttle control system. The larger 90-mm throttle opening and four-bolt pattern requires an intake manifold upgrade or an adapter plate. Aftermarket wire harness adapters are available for a plug-and-play installation.

The LS1 Corvette throttle body was the first electronic throttle body used with Chevrolet V engines. The throttle position sensor is mounted on the bank 2 side of the engine and the throttle shaft motor is mounted on the bank 1 side of the engine. The blade on this throttle body measures approximately 75 mm in diameter.

The LS2 and early LS3 Corvette throttle body is an electronically compatible alternative to the smaller LS1 throttle body. The blade on this throttle body measures approximately 90 mm in diameter. Because the bore is larger and the four-bolt pattern is different than the three-bolt pattern of the LS1 intake manifold, the use of this throttle body requires a different intake manifold or adapter plate.

The Corvette PCM and TAC monitor values from the two throttle position signals to identify proper operation of the throttle body. A DTC sets if a TPS value exceeds one of GM’s predetermined threshold values. This chart reviews the allowable operating ranges for each TP sensor (see “TPS Failure”) and the expected 0-percent and 100-percent voltage ranges for each TP sensor.

This wiring diagram represents the 1997–2004 Corvette electronic throttle control system with LS2 throttle body. Notice the 5V reference and low reference for TP sensor 2 is not used because TP signal 1 and TP signal 2 share the same 5V reference and low reference from the TAC module.

This bench test of the LS2 throttle body demonstrates the electronic compatibility with the 1997–2004 Corvette electronic throttle system.

The Corvette PCM and TAC monitor values from the three accelerator position signals to identify proper operation of the accelerator pedal assembly. A DTC sets if an APP value exceeds one of GM’s predetermined threshold values. This chart reviews the allowable operating ranges for each APP sensor (see “APP Failure”) and the expected 0- and 100- percent voltage ranges for each APP sensor

Pedal Assembly

The LS1/LS6 Corvette accelerator pedal assembly has an APP sensor that contains three APP signals. The TAC module uses the three APP signals to determine absolute pedal position. APP sensor 1 signals voltage increases as the pedal is depressed. APP sensor 2 and sensor 3 signal voltage decreases as the pedal is depressed. The APP sensor signals are used by the PCM to monitor and make available one accelerator pedal percent PID.

The C5 Corvette (1997–2004) used only one accelerator pedal assembly. It is very popular because of its size and mounting configuration.

Throttle Actuator Control Module

There have been a few part number changes for the 1997–2004 Corvette TAC module but the Corvette TAC modules are interchangeable and General Motors maintains only one current part number for all 1997–2004 TAC modules. The Corvette TAC module looks identical to the 1999–2002 GM Truck TAC module, and even has the same harness connections, but carries a different GM part number and is not interchangeable with GM trucks.

The 1997–2004 Corvette and 2004–2005 Cadillac CTS-V use the same TAC module. Although these vehicles use a different accelerator pedal assembly and TAC-to-pedal wire harness, electronic throttle equipment can be used interchangeably among these vehicles.

2004–2005 Cadillac CTS-V

The 2004–2005 Cadillac CTS-V has much in common with the LS6 Corvette. General Motors used the Corvette TAC module, 2004 PCM (GM# 12586243), and LS1/LS6 throttle body with the LS6 CTS-V. In the same way that the LS1/LS6 Corvette can use the 2005–2008 LS2/LS3 throttle body, the LS6 CTS-V can use the 2005–2008 LS2/LS3 Corvette throttle body as a performance upgrade.

The CTS-V PCM and TAC monitor values from the three accelerator position signals to identify proper operation of the accelerator pedal assembly. A DTC sets if an APP value exceeds one of GM’s predetermined threshold values. This chart reviews the allowable operating ranges for each APP sensor (see “APP Failure”) and the expected 0- and 100-percent voltage ranges for each APP sensor.

The 2004–2005 Cadillac CTS-V accelerator pedal assembly is unique. What is worth noting for Gen IV systems is that this pedal assembly uses the same housing (but a different harness connector) as some of the common LS-series applications (such as LS2 Trailblazer SS and Chevrolet Performance LS2/LS3/LS7 kits).

This wiring diagram represents the 2004–2005 Cadillac CTS-V electronic throttle control system. Notice the only difference between the CTS-V and 1997–2004 Corvette is the accelerator pedal assembly and TAC-to-pedal wire harness.

Pedal Assembly

Even though a different accelerator pedal assembly was used with the 2004–2005 CTS-V, its APP sensor functions in similar ways to the 1997–2004 Corvette APP sensor. APP sensor 1 signals voltage increases as the pedal is depressed. APP sensor 2 and APP sensor 3 signal voltage decreases as the pedal is depressed. The APP sensor signals are used by the PCM to monitor and make available one accelerator pedal percent PID. Be careful to use a matching accelerator pedal and TAC-to-pedal wire harness. The Corvette harness does not work with the CTS-V accelerator pedal.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

GM Truck

In general, trucks with a Gen III engine have two different electronic throttle configurations: 1999–2002 and 2003–2007. However, a careful look at the Gen III electronic throttle systems used in GM trucks from 1999–2007 reveals four specific configurations.

1999–2002

Throttle Body: The truck throttle body is fitted with a TPS to monitor throttle blade angle and a motor, operated by the TAC module, to open and close the throttle blade. The TPS housing contains two individual sensors with separate signal, low reference, and 5V circuits. The two TPS signals are monitored by the TAC module. As the throttle blade is opened, TPS sensor 1 voltage sweeps toward 5V reference and TPS sensor 2 voltage sweeps toward low reference. These opposing signals are used by the PCM to monitor and make available one throttle angle PID.

The GM truck throttle body looks much like the 1997–2004 Corvette throttle body but with the TPS and throttle shaft motor on opposite sides. The truck and Corvette share the same throttle shaft motor (which is not serviceable separately) but with opposing polarity. The blade on this throttle body measures approximately 75 mm in diameter.

Pedal Assembly: The 1999–2002 truck accelerator pedal assembly contains an APP sensor that contains three APP signals. The TAC module uses the three APP signals to determine absolute pedal position. APP sensor 1 signals voltage increases as the pedal is depressed. APP sensor 2 and sensor 3 signal voltage decreases as the pedal is depressed. The APP sensor signals are used by the PCM to monitor and make available one accelerator pedal percent PID.

The GM truck pedal introduced in 1999 was used through 2005. There is an adjustable pedal assembly but the APP sensor is the same. The 1999–2002 systems use all three of the APP signals while the 2003–2005 systems use only two of the three APP signals.

This wiring diagram represents the 1999–2002 GM truck electronic throttle control system. This is the only GM truck system that uses the three APP sensors in the accelerator pedal. Later systems use two APP sensors.

Throttle Actuator Control Module: The 1999–2002 truck TAC module is specific to 1999–2002 trucks and must use a 1999–2002 truck PCM. The truck TAC module looks identical to the 1997–2004 Corvette TAC module, and even has the same harness connections, but carries a different GM part number and is not interchangeable with the Corvette.

This is the 1999–2002 GM truck TAC module. It looks identical to the 1997–2004 Corvette TAC module but it is not interchangeable with other electronic throttle systems.

2003–2004

In 2003, General Motors introduced a new Gen III truck throttle body, TAC module, and PCM. This new throttle body is not backward compatible with the 1999–2002 trucks. Always use matching equipment to ensure compatibility.

This wiring diagram represents the 2003–2004 GM Truck electronic throttle control system. This system uses only two of the three APP sensors. As compared to the 1999–2002 GM truck TAC module, the 5V reference and low reference for APP sensor 2 have been swapped. Although 2003–2004 GM trucks use only two of the three APP sensors, the 2003–2004 TAC-to-pedal wire harness contains the three wires for APP sensor 3. This is probably a carry-over from 1999–2002 GM stock.

The GM truck PCM and TAC monitor values from the three accelerator position signals to identify proper operation of the accelerator pedal assembly. A DTC sets if an APP value exceeds one of GM’s predetermined threshold values. This chart reviews the allowable operating ranges for each APP sensor (see “APP Failure”) and the expected 0- and 100-percent voltage ranges for each APP sensor.

The GM truck PCM and TAC monitor values from the two throttle position signals to identify proper operation of the throttle body. A DTC sets if a TPS value exceeds one of GM’s predetermined threshold values. This chart reviews the allowable operating ranges for each TP sensor (see “TPS Failure”) and the expected 0-percent range and 100-percent limit voltages for each TP sensor.

The GM truck PCM and TAC monitor values from two of the three accelerator position signals to identify proper operation of the accelerator pedal assembly. A DTC sets if an APP value exceeds one of GM’s predetermined threshold values. This chart reviews the allowable operating ranges for each APP sensor (see “APP Failure”) and the expected 0-percent range and 100-percent limit voltages for each APP sensor.

The 2003–2007 truck TAC modules are interchangeable. This TAC module uses the same wire harness connectors as 1999–2002 GM trucks, with an aluminum back plate and smooth plastic cover, but the housing looks very different.

Throttle Body: The 2003 throttle body was used with Gen III trucks from 2003 to 2007. The truck throttle body is fitted with an internal TPS to monitor throttle blade angle and an internal motor, operated by the TAC module, to open and close the throttle blade. The throttle body contains two individual TP sensors with separate signal, low reference, and 5V circuits. The two TP signals are monitored by the TAC module. As the throttle blade is opened, both TP sensor 1 and TP sensor 2 signal voltages sweep toward 5V reference. These signals are used by the PCM to monitor and make available one throttle angle PID.

Pedal Assembly: The 2003–2004 truck accelerator pedal assembly is the same as used with 1999–2002 trucks. With an option for an adjustable pedal assembly, the APP sensor is the same. The TAC module uses only two of the three APP signals to determine absolute pedal position. A change from the 1999–2002 truck TAC system is that both APP sensor 1 and APP sensor 2 signal voltage increases as the pedal is depressed. APP sensor 3 is no longer used by the 2003–2007 truck TAC modules, but the 2003–2004 TAC-to-pedal harnesses contain the three wires once used for APP sensor 3 (as found in 1999–2002 truck TAC-to-pedal harnesses). The APP sensor signals are used by the PCM to monitor and make available one accelerator pedal percent PID.

This wiring diagram represents the 2005 GM truck electronic throttle control system. Just like the 2003–2004 GM truck system, only two of the three APP sensors are used. By 2005 you should not expect to see the unused three wires for APP sensor 3.

This wiring diagram represents the 2006–2007 GM truck electronic throttle control system. As shown in this schematic, the introduction of a new accelerator pedal assembly means a different TAC-to-pedal wire harness.

The GM truck PCM and TAC monitor values from two accelerator position signals to identify proper operation of the accelerator pedal assembly. A DTC sets if an APP value exceeds one of GM’s predetermined threshold values. This chart reviews the allowable operating ranges for each APP sensor (see “APP Failure”) and the expected 0-percent range and 100-percent limit voltages for each APP sensor.

Throttle Actuator Control Module: The 2003–2004 truck TAC modules are interchangeable with 2005–2007 truck TAC modules. With an aluminum back plate and smooth plastic housing, this truck TAC module has an appearance different from the 1999–2002 truck TAC modules. The harness connections at the TAC module are the same, but the 1999– 2002 truck engine wiring harnesses are not directly compatible with the 2003–2007 Gen III trucks.

2005

The 2005 truck electronic throttle system uses the same throttle body, TAC module, PCM, and accelerator pedal as the 2003–2004 trucks, but the non-use of APP sensor 3 shows itself with the removal of the three APP sensor 3 wires in the TAC to-pedal harness. The 2003–2005 TAC-to-pedal harnesses can be used interchangeably because APP sensor 3 is not used by the 2003–2007 truck TAC module.

2006–2007

The 2006–2007 Gen III truck electronic throttle system uses the same throttle body, TAC module, and PCM as the 2003–2005 trucks. The only change in 2006 was a new accelerator pedal assembly. All other electronic throttle system components are interchangeable with 2003–2005 trucks.

This accelerator pedal assembly is used with 2006–2007 GM trucks and is functionally interchangeable with the 2002–2005 system. A matching TAC-to-pedal wire harness is required.

Pedal Assembly: Although smaller in size, the 2006–2007 truck accelerator pedal assembly is functionally the same as the 2003– 2005 assembly. Containing only the required two APP sensors, the harness connection on this pedal assembly uses only six wires. The 2003–2005 accelerator pedal assembly contains three APP sensors, but only two are used, leaving three connector cavities unused (as is found in 2005 truck TAC-to-pedal harnesses). The TAC module uses the two APP signals to determine absolute pedal position. Both APP sensor 1 and APP sensor 2 signal voltage increases as the pedal is depressed. The APP sensor signals are used by the PCM to monitor and make available one accelerator pedal percent PID.

EFI Connection 24x Throttle Body Assemblies

Bringing LS fuel management to early small- and big-block Chevrolet engines requires an electronic throttle body assembly that fits the early fuel injection intake manifolds. EFI Connection’s solution was to use the 1997–2004 LS1/LS6 Corvette throttle body, but within a new housing designed for TPI and LT1 intake manifolds.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

Offered with twin 52-mm blades, twin 58-mm blades, or an oval mono blade, an electronic throttle body solution is available for any intake manifold using the popular TPI/ LT1-type four-bolt pattern. All three throttle bodies are machined from a solid block of 6061 T6 heat-treated aluminum. The throttle blade shaft is supported by sealed ball bearings for longevity and the throttle blades are CNC machined, rather than being stamped, for a precise fit. These CNC-manufactured throttle bodies are among the highest quality from the aftermarket.

EFI Connection’s lineup of electronic throttle bodies for TPI, LT1, and Ram Jet 502 are available in common sizes: 52 mm, 58 mm, and oval mono blade.

This EFI Connection 58-mm electronic throttle body flows approximately 1,100 cfm making it appropriate for engines making 480 to 600 hp.

This 52-mm electronic throttle body is installed on a TPI engine. The TPI plenum was slightly ported to line up with the 52-mm throttle bore openings. Flowing approximately 920 cfm, this throttle body is adequate for engines making 325 to 480 hp.

This Ram Jet 502 engine receives much more air with this mono blade electronic throttle body. With an LS1 Corvette- based electronic throttle system and PCM, this engine has much more to offer than it did with the bundled MEFI (marine electronic fuel injection) ECU and 48-mm cable throttle body. This mono-blade throttle body flows approximately 1,250 cfm and is a good choice for engines making more than 600 hp.

52-mm TPI/LT1 Throttle Body

EFI Connection’s 52-mm electronic throttle body is intended to be used on stock to mild small-block engines. With nearly 920 cfm of airflow, this throttle body is good for engines making 325 to 480 hp. Most intake manifolds with the dual-bore, TPI-type throttle openings require minor port matching for smooth airflow transition from the throttle body into the intake plenum.

58-mm TPI/LT1 Throttle Body

EFI Connection’s 58-mm electronic throttle body is intended to be used on mild to aggressive small- and big-block engines. With nearly 1,100 cfm of airflow, this throttle body is good for engines making 480 to 600 hp. This throttle body requires port matching for smooth airflow transition and throttle blade clearance into the intake plenum.

Mono Blade TPI/LT1 Throttle Body

EFI Connection’s mono blade electronic throttle body is intended to be used on maximum-effort small-and big-block engines. With nearly 1,250 cfm of airflow, this throttle body is good for engines making more than 600 hp. This throttle body require port matching for smooth airflow transition and throttle blade clearance into the intake plenum.

Written by Mike Noonan and Posted with Permission of CarTechBooks

LEARN MORE ABOUT THIS BOOK

If you liked this article, you will LOVE the full book!
Get your copy here.

The post GM Gen III LS PCM/ECM: Electronic Throttle Equipment Guide appeared first on LS Engine DIY.

GM Gen III LS PCM/ECM: How to Change the Firing Order

LS Engine DiY — Sat, 14 Feb 2015 07:18:41 +0000

Let’s begin this chapter by agreeing that the “LS1 PCM” is just an ECU that has the designed purpose of controlling the sequencing of ignition and injector events based on a variety of sensor inputs. We can then agree that this ECU is uniquely programmed so that combustion results are favorable so that the stoichiometric ratio of air to fuel (approximately 14.7 to 1) is achieved during normal operating conditions (and so on). Simply put, the ECU can be calibrated for any V-6 or V-8 engine because General Motors designed it that way.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

Injectors and Ignition Coils

A very common question goes something like this, “How can I use the LS1 PCM on my Gen I small-block engine when the firing order between the two engines is different?” To answer this question, let’s take a look at how General Motors addressed this issue.

In model year 2001, General Motors released Gen I small-block and LS-series engines that all used the same PCM (GM# 12200411). The firing order for the Gen I small-block engine is 1-8- 4-3-6-5-7-2. The firing order for the LSseries engines is 1-8-7-2-6-5-4-3. Notice that cylinders 4 and 7 have swapped, and cylinders 3 and 2 have swapped. When you compare this PCM’s fuel injector wiring diagrams for the Gen I small-block with the LS-series engines, you see something interesting: General Motors simply swapped injector outputs 4 and 7, and 3 and 2 within the engine wire harness to address the firing order change.

Not all GM V-8 engines have the same firing order. This chart compares the order for five engine families. Notice that cylinders 4 and 7 and 3 and 2 are swapped for early small-/big-block engines and late small-/big-block engines.

This schematic represents proper wiring of the eight fuel injectors for Gen I small-block, Gen II LT1, and Gen VI big-block engines with the firing order 1-8-4-3-6-5-7-2.

This schematic represents proper wiring of the eight fuel injectors for Gen III and Vortec 8100 8.1L big-block engines with the firing order 1-8-7-2-6-5-4-3.

This EFILive table represents the assignment of fuel injectors to their proper cylinder in the
engine firing order. These particular table values were taken from a 2001 5.7L Express Van.

This EFILive table represents the assignment of fuel injectors to their
proper cylinder in the engine firing order. These particular table values were taken from a 2001 LS1 Corvette.

This schematic represents proper wiring of the eight ignition coils for Gen I small-block, Gen II LT1, and Gen VI big-block engines with the firing order 1-8-4-3-6-5-7-2.

This schematic represents proper wiring of the eight ignition coils for Gen III and Vortec 8100 8.1L big-block engines with the firing order 1-8-7-2-6-5-4-3.

Now compare this PCM’s fuel injector calibration details for the Gen I small-block and LS-series engine. EFILive reveals that General Motors also changed the injection bank assignments table values to follow the wire harness fuel injector assignments. The PCM must be calibrated to know which injectors are assigned to bank 1 (cylinders 1, 3, 5, 7) and bank 2 (cylinders 2, 4, 6, 8) so that fuel trims are applied to the proper bank of cylinders. If the injection bank assignments are wrong, fuel trims are extreme and the engine runs poorly and may even stall.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

Although the PCMs are the same, the ignition systems are different. Gen I Vortec V-8 engines use a four-pulse, low-resolution, crankshaft signal for single coil and distributor ignition. LS-series engines use a 24-pulse (24x), high-resolution, crankshaft signal for coil-per-cylinder ignition. However, the same logic applies here if using a Gen I small-block engine with the LS-series engine’s 24x crankshaft signal. The wire harness requires that ignition coil assignments for cylinders 4 and 7, and 3 and 2 be swapped.

DTCs are assigned to ignition coil control circuits. The calibration table for the assignment of these DTCs is not available within most tuning software packages. A changed firing order may result in an incorrect DTC notification.

For instance, let’s say you have a PCM from a 2001 Camaro with the LS1 engine. You installed a 24x conversion on the Gen I small-block and made the necessary wire harness and injection bank assignment updates. During engine operation, the PCM determines that the ignition coil 4 control circuit has shorted to a voltage. The DTC P0357 for cylinder 7 is set. Because the firing order has changed, and the ignition coil control circuit firing order diagnostics table has not been updated, this DTC actually represents cylinder 4 because of the firing order difference between a Gen I small-block and LS1 engine.

Modifying Calibration

To begin, open your previously saved calibration file or read the current calibration stored in your PCM (press Ctrl+ Pg+ Up). Once your calibration file is open in EFILive, access the Injection Bank Assignments table by expanding Engine Calibration, expanding Fuel, expanding Injectors, and then selecting the Injection Bank Assignments table.

For each fuel injector (labeled A through H in no particular order), the table indicates which bank of cylinders (bank 1 or 2) the fuel injector is located in. Bank 1 represents cylinders 1-3-5-7, and bank 2 represents cylinders 2-4-6-8. Notice all odd injectors are assigned to bank 1 and all even injectors are assigned to bank 2.

Let’s first look at the injection bank assignments for an LS1 engine. (See Figure 7.1.) The firing order for Gen III engines is 1-8-7-2-6-5-4-3. Because the engine firing order begins with cylinder 1, the injection bank assignments table uses Injector A to represent the fuel injector located at cylinder 1.

Moving along with the firing order, the fuel injector located at cylinder 8 is represented as Injector B, the fuel injector at cylinder 7 is represented as Injector C, the fuel injector at cylinder 2 is represented as Injector D, the fuel injector at cylinder 6 is represented as Injector E, the fuel injector at cylinder 5 is represented as Injector F, the fuel injector at cylinder 4 is represented as Injector G, and the fuel injector at cylinder 3 is represented as Injector H.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

Now let’s look at an engine with a different firing order, the Gen I small-block. This firing order is 1-8-4-3-6- 5-7-2. Just as with the LS1 example above, you see that the fuel injector at cylinder 1 is represented as Injector A and along the engine firing order through cylinder 8 represented by Injector H. Once again, all odd injectors are assigned to bank 1, and all even injectors are assigned to bank 2.

Six-cylinder engines do not use this entire table. If you were to open a calibration file from a 2001 S10 4.3L PCM (see Figure 7.1), you would see values for the last two injectors, G and H. (See Figure 7.2.) This is because the “LS1 PCM” is simply an ECM that is calibrated for the engine in which it is being used.

This chart represents the assignment of cylinders (A through L) to DTCs (P0351 through P0362) for proper ignition coil control circuit malfunction detection. If an ignition coil control circuit is open or shorted, the PCM uses this table to assign the appropriate DTC. Some OBD-II vehicles have engines with more than eight cylinders, so OBD-II systems have reserved DTCs P0351 through P0362 for ignition coil control circuit malfunction detection. The LS1 PCM never reports DTCs P0359 through P0362 because cylinders 9 through 12 are not supported.

The injection bank assignments table must follow the wiring of the fuel injectors to the PCM. If the engine firing order changes and this table is not updated, fuel trims are extreme and eventually cause the engine to stall. The values represented here were taken from a 2001 LS1 Corvette.

Fig. 7.1. The LS-series engines have a different firing order than the early small-block and LT1 engines. Cylinders 2 and 3 and 7 and 4 have been swapped in the engine firing order. When using an LS-series engine calibration (24x crank signal) with an early small-block or LT1 engine, the injection bank assignments table must be updated. Notice the difference between the injection bank assignments for an LS-series and early small-block or LT1 engine.

Fig. 7.2. The injection bank assignments for a 4.3L V-6 are displayed as though there are eight injectors because the table is provisioned for eight cylinders. However, the PCM knows to use only the first six injector assignments when using a calibration for a 4.3L V-6 engine.

For the injection bank assignments table to exist in the PCM’s memory space, it must be dimensioned. A programmer must define the size (memory space) that an object (such as a table or constant) requires. In this case, General Motors intended for this injection bank assignments table to be used with an engine that contains no more than eight cylinders. This is why the table displays eight injectors for a calibration file written for an engine with only six cylinders. (Had General Motors written a calibration file for a PCM for an engine with four cylinders, the table would also display eight injectors.)

This is simply a lookup table as the PCM knows (from elsewhere) that this engine has six cylinders, is using a low-resolution 3x crankshaft signal to know engine position, and to fire injectors once every 60 degrees of crankshaft rotation. The last two injectors represented in this table are simply ignored when the PCM looks for injection bank assignments. The firing order for this 4.3L V-6 engine is 1-6-5-4-3-2.

Again, begin with the fuel injector at cylinder 1 being represented as Injector A and move along the engine firing order through cylinder 6 represented by Injector F. Here also, all odd injectors are assigned to bank 1, and all even injectors are assigned to bank 2. The value of Injector G and Injector H are ignored.

Written by Mike Noonan and Posted with Permission of CarTechBooks

LEARN MORE ABOUT THIS BOOK

If you liked this article, you will LOVE the full book!
Get your copy here.

The post GM Gen III LS PCM/ECM: How to Change the Firing Order appeared first on LS Engine DIY.

Upgrading to Gen III LS-Series PCM: Signal Output Guide

LS Engine DiY — Fri, 13 Feb 2015 18:55:45 +0000

Production GM vehicles rely on the PCM to provide signal outputs to control the engine, gauges, electric fans, emissions equipment, air conditioning, and other equipment.

Engine Control Output

The basic purpose of any engine computer is to correctly deliver fuel and initiate ignition events for any engine operating condition. To do this correctly, engines are fitted with many sensors that provide measurable real-time operating data. Combined with calibrated parameters, the sensor values are used by the engine computer to activate the injector and ignition-coil control signals.

LS-series ignition coils are interchangeable. As an example, you can swap a 2002 Corvette ignition coil bracket assembly (ignition coils, mounting bracket, and coil harness) with a 2008 Corvette ignition coil bracket assembly. General Motors has designed each ignition coil pack harness to be universal to any LS-series engine wire harness. General Motors has used a variety of ignition coils with LS-series engines. GM# 12558948 ignition coil (bottom left) is only used with the LS1 and LS6 engine in the Camaro, Firebird, Corvette, and Cadillac CTS-V. GM# 12573190 ignition coil (middle left) and GM# 12611424 ignition coil (top left) are used with 2005-newer cars, trucks, and vans. GM# 10457730 ignition coil (bottom right) and GM# 12558693 (top right) are used with
1999–2007 trucks and vans.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

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Ignition Coils

All Gen III engines are fitted with eight ignition coils. Each coil is responsible for delivering spark to its assigned cylinder. The engine computer must determine spark angle, or degrees Before Top Dead Center (BTDC), to activate each ignition coil through the ignition control (IC) circuit. As part of this complicated calculation, the engine computer considers engine speed (CKP input), coolant temperature (ECT input), intake air temperature (IAT input), knock sensor values (KS input), throttle position (TPS input), vehicle speed (VSS input), transmission gear (P/N input), and more. To prevent weak spark, the engine computer also controls the ignition coil charge time (or dwell time) before firing. (See Figure 6.1.)

LS-Series Ignition Coil Output LS-series engines have eight individual coils. To release a coil’s charge when an ignition event is requested, the engine computer commands the IC coil output circuit low (toward 0V). This energizes the ignition coil and causes the spark plug to produce spark. All ignition coils on LS-series engines operate in the same way. Changing a set of eight ignition coils for a different set of eight ignition coils may require (or at the very least, benefit from) changes to the engine computer’s spark calibration, including the spark dwell timetable. (See Figure 6.1.)

Fig. 6.1. This table represents lookup values for the amount of time the ignition coils are charged before the PCM sends a signal to fire them. If the dwell time is too long, the ignition coils may overheat. If the dwell time is too short, a weak spark (and loss of power) may result.

This LS1 and LS6 GM coil bracket assembly is installed on all 1999-newer LS1 and LS6 engine valve covers. A coil bracket assembly includes a formed steel bracket, four ignition coils, and a wire harness. With a variety of LS-series ignition coils, not all coil mounting positions and brackets are the same. However, General Motors has designed all coil pack wire harnesses to universally plug into any LS-series engine wire harness.

EFI Connection offers a coil bracket assembly that uses GM# 12573190 ignition coils. The coil bracket cleanly fits Gen I small-block and Gen II LT1 engine center bolt valve covers. The layout allows clearance for oil fill, PCV, and breather. The wire harness is specific to the bracket and ignition coil layout, but universally plugs into any LS-series engine wire harness. For engines with perimeter-bolt valve covers, bosses can be welded to the surface of the valve cover for attachment.

Since 1996, the Vortec V-6 and Vortec V-8 engines have used a single coil, ignition module, and distributor. The 2001–2002 GM vehicles with Vortec V-6 and Vortec V-8 engines use the same PCM (GM# 12200411) as the vehicles with LS-series engines. Engine operation requires a four-pulse (for V-8) crankshaft signal (reluctor and sensor at bottom), one-pulse camshaft signal from within a Vortec distributor (right), a single coil and ignition module (middle), GM# 12200411 PCM (left), and a base PCM calibration that supports a low-resolution crankshaft signal with single coil and distributor (like a 2001 5.7L Express Van calibration). Vortec V-6 engines require a three-pulse crankshaft signal and supporting PCM calibration (like a 2001 4.3L S-10 calibration).

Fig. 6.2. The V-8 and V-6 Vortec ignition system components have remained unchanged since 1996. All 1996-newer Vortec V-8 and V-6 engines use the same ignition module, ignition coil, CKP sensor, and CMP sensor. Due to the variations in engine size, and for accuracy, several different knock sensors have been used. Because only the PCM has been changed throughout the years, the 2001-2002 Gen III PCM (GM# 12200411) may be used with any 1996-newer V-8 and V-6 Vortec engine.

Vortec V-6 and Gen I Small-Block Vortec V-8 Ignition Coil Output: The only Gen III PCM that General Motors used with the Vortec V-6 and Gen I small-block Vortec V-8 engines is the 2001–2002 (GM# 12200411). These engines only offer single coil and distributor ignition. Comparing wire schematics between an LS-series engine and Vortec V-6 or Vortec V-8 engine reveals that the same IC circuit controlling ignition coil 1 on the LS-series engines is used to control the ignition control module (ICM) of the Vortec V-6 and Gen I small-block Vortec V-8 engines. (See Figure 6.2.) The ICM causes the ignition coil to fire based on IC circuit signal pulses.

Fuel Injector Control

By 1996 all GM V-6 and V-8 engines were fitted with one injector for each cylinder. The engine computer controls each fuel injector through an internal switch (or driver), which applies a ground signal to each fuel injector. With 12V ignition power at each injector while the engine is running, the fuel injector driver applies ground, opening each injector to allow fuel to pass through the injector and into the engine cylinder The engine computer controls the pulse width (or duration) and sequencing of each injector driver. The engine computer determines fuel injector sequencing based on crankshaft position (CKP) and camshaft position (CMP). Pulse widths are calculated from inputs such as air mass (MAF input), manifold pressure (MAP input), throttle position (TPS input), intake air temperature (IAT input), coolant temperature (ECT input), engine speed (CKP input), and more.

The firing order is hardwired to the engine computer, but the bank assignment of each injector is defined within the engine computer’s calibration. (See Chapter 7 for more about the firing order.)

Fuel Pump Relay Control

The fuel pump is controlled by the engine computer through a relay. The relay coil is grounded and the engine computer supplies a 12V power source to the relay coil. This switches battery power to the fuel pump. When the ignition switch is turned to the ON position, the PCM cycles the fuel pump on for several seconds to pressurize the fuel rails. The fuel pump only runs when the engine computer sees a signal from the CKP sensor indicating that the crankshaft is rotating.

The fuel pump is turned on through a relay because the PCM cannot handle the current. When the ignition key is turned on, the PCM turns the fuel pump relay on for several seconds to prime the fuel system. The PCM does not command the fuel pump to run again until a signal is received from the CKP sensor.

The PCM controls the illumination of the MIL by applying a ground to the bulb. Ignition power is received at the bulb from the gauges fuse. The MIL is important because it may be the first indicator
that there is a problem with engine or transmission performance.

The PCM uses the VSS and calibration data to determine how many pulses to output for each of the VSS outputs. Most production GM vehicles only use the primary VSS output, which is most often used for the speedometer. The secondary VSS output, for example, can be used with any third-generation F-Body to satisfy the 2,000-pulse-per-mile cruise control module VSS signal input requirement.

The PCM calculates engine speed(RPM) based on the signal it receives from the CKP sensor. The RPM signal is then output to the tachometer.

Malfunction Indicator Lamp Control

Knowing that a malfunction is occurring (or has occurred) can be critical. The malfunction indicator lamp (MIL) in the instrument cluster is used to indicate that a malfunction has occurred. In a production GM vehicle, the MIL receives 12V power through the gauges fuse. The engine computer applies a ground to. the control circuit to illuminate the lamp. When the cause of a malfunction has been fixed, the MIL can be reset by clearing stored DTCs or by running the engine or transmission through several cycles as defined in the calibration.

Tachometer Output

The engine computer provides a tachometer output for monitoring engine speed. For LS-series engines, one revolution per minute (RPM) equals one set of 24 crankshaft signal pulses. For Gen I small-block Vortec and Gen VI big-block Vortec engines, one rpm equals one set of four crankshaft signal pulses. For Vortec V-6 engines, one rpm equals one set of three crankshaft signal pulses. The engine computer calibration allows for adjustment to the output signal for compatibility with many tachometers.

The number of output pulses for the tachometer is configurable. As shown here, the tachometer in a 2002 LS1 Camaro instrument cluster requires the Tacho Pulses High and Tacho Pulses Low values of “6.” As another example, a Gen III PCM installation into an LT1 Camaro requires Tacho Pulses High and Tacho Pulses Low values of “3” and Tacho Pullup Enable set to “Yes.”

Vehicle Speed Output

Two VSS outputs are available with Gen III PCMs. These VSS outputs are defined in the PCM calibration as primary and secondary. For production GM vehicles, the primary VSS output is often used for the speedometer and the secondary VSS output is often used for the antilock brake system (ABS). The pulse count for each VSS output is configurable within the PCM calibration.

Electric Fan Control

While all Gen III PCMs support electric fan control, not all production GM vehicles with a Gen III PCM have electric fans. The PCM controls two output signals based on coolant temperature (ECT input), vehicle speed (VSS input), and air conditioning inputs. General Motors uses these two outputs with three relays to operate two electric fans in low/ high-speed operation by switching between series and parallel operation. (See Chapter 11 for more information about electric fan operation.)

Speedometer > Parameters, you find the primary VSS output (calibration {H0105}) and the secondary VSS output (calibration {H0106}). These values should be set after the VSS tooth count, tire size, and gear ratio have been properly set in the PCM calibration file." width="600" height="521" srcset="https://www.lsenginediy.com/wp-content/uploads/2015/02/124.jpg 600w, https://www.lsenginediy.com/wp-content/uploads/2015/02/124-300x260.jpg 300w" sizes="auto, (max-width: 600px) 100vw, 600px" />

Using EFILive, from Calibration > Speedometer > Parameters, you find the primary VSS output (calibration {H0105}) and the secondary VSS output (calibration {H0106}). These values should be set after the VSS tooth count, tire size, and gear ratio have been properly set in the PCM calibration file.

Speedometer > Parameters > Speedo Calculator. The Speedo Calculator tab presents tire size, gear ratio, and number of teeth on the VSS pickup reluctor. The Sprocket Ratios tab is related to front-wheel- drive transmissions. The Speedo Fine Tuning tab is most accurately used while the vehicle is on a chassis dyno to make fine adjustments to the value displayed on the speedometer." width="600" height="555" srcset="https://www.lsenginediy.com/wp-content/uploads/2015/02/133.jpg 600w, https://www.lsenginediy.com/wp-content/uploads/2015/02/133-300x277.jpg 300w" sizes="auto, (max-width: 600px) 100vw, 600px" />

EFILive’s Speedo Calculator is accessed from Calibrations > Speedometer > Parameters > Speedo Calculator. The Speedo Calculator tab presents tire size, gear ratio, and number of teeth on the VSS pickup reluctor. The Sprocket Ratios tab is related to front-wheel-drive transmissions. The Speedo Fine Tuning tab is most accurately used while the vehicle is on a chassis dyno to make fine adjustments to the value displayed on the speedometer. The Shift Point Correction tab allows a percentage adjustment to the shift tables after a tire size or gear ratio change.

This tech tip is from the full book, HOW TO USE AND UPGRADE TO GM GEN III LS-SERIES POWERTRAIN CONTROL SYSTEMS.

For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE

SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://www.lsenginediy.com/upgrading-gen-iii-ls-series-pcm-signal-output-guide/

Air Conditioning Control

The PCM is solely responsible for controlling the A/C compressor clutch through a relay. The A/C compressor clutch relay coil and switch receive 12V ignition power with the key in the ON position. Based on the A/C request input, A/C compressor clutch supply voltage input, A/C pressure sensor input, engine speed (RPM input), throttle angle (TPS input), and intake air temperature (IAT input), the PCM applies a ground to the control circuit to switch 12V power to the A/C compressor clutch. (See Chapter 11 for more information about A/C operation.)

Generator Control

Gen III PCMs have the ability to control generator load on the engine through a turn-on signal output. In addition, some vehicles use a generator field duty cycle signal input to the PCM to monitor the duty cycle (ON/OFF) of the generator. Generator load on the engine is calculated based on a PWM signal from the generator. Many conversions disable PCM generator control, but it may be beneficial to retain or enable this feature to adjust engine idle speed to compensate for high generator loads.

Production vehicles with Gen III PCMs use the PCM to control the generator. Although the generator turn-on signal output is always used, the generator field duty cycle signal is not. Most commonly the Camaro and Firebird use only the generator turn-on signal; trucks and vans use both the generator turn-on signal and the generator field duty cycle signal; the Corvette uses both PCM signals plus a 16-gauge battery wire (in generator connector cavity A). Be sure to consider which generator you are working with and your instrument panel charge lamp requirement when wiring your generator.

When the PCM is not used to control the generator, there are a few DTCs that need to be disabled. There are two parts to disabling these DTCs: processing enablers and MIL enablers. By setting DTCs P1637 and P1638 to “Not Reported” within the processing enablers, the PCM ignores the processing of these DTCs.

By setting DTCs P1637 and P1638 to “No MIL” within the MIL enablers, the PCM does not apply ground to the MIL control circuit (the MIL does not illuminate).

Although the PCM is capable of controlling AIR, EGR, and EVAP, using the PCMs emissions controls does not necessarily mean emissions compliance in your state or county. Before removing emissions equipment, check with your local emissions laws. Removing emissions components also requires turning off (or disabling) the DTC processing enablers and DTC MIL enablers within the PCM calibration.

When the PCM is not used to control the generator, DTCs P1637 and P1638 need to be disabled. If you forget to disable these DTCs, they appear in the list of active DTCs when you scan the PCM through the DLC.

Emissions Control

Gen III PCMs are emissions control capable, but may not be emissions compliant. Your state has specific emissions laws for on-road vehicles that you must adhere to for emissions compliance. After checking with your local emissions testing station, you may find that emissions compliance for your conversion simply means adding a charcoal canister and purge line, or you may find that emissions compliance requires all relevant emissions control of your engine’s original vehicle.

EVAP Canister Purge Solenoid

Today’s vehicles are equipped with an evaporative emissions (EVAP) control system. Its primary function is to control a charcoal canister purge solenoid. This canister stores fuel vapor and is connected to the fuel tank through a hose.

The engine computer controls the purge solenoid during engine operation to purge the charcoal canister of fuel vapor. Intake manifold vacuum pulls the fuel vapor from the charcoal canister so it can be burned in the combustion process. The PCM applies logic to the operation of the purge solenoid so the purge routine does not create a rich or lean condition.

The PCM checks EVAP purge solenoid performance by monitoring fuel tank pressure (or vacuum) through the fuel tank pressure sensor. If fuel tank vacuum is more than expected within a predetermined amount of time, the PCM knows that the EVAP purge solenoid is leaking engine vacuum to the fuel tank and sets a DTC.

EVAP Canister Vent Solenoid

The EVAP vent valve allows fresh air to enter the EVAP canister. The vent valve is normally open, but is closed when the PCM-controlled vent solenoid is activated. Closing the vent valve allows the PCM to test the EVAP lines for any leaks. To activate the vent solenoid, the PCM applies a ground.

EGR Solenoid Control and Valve Position Signal

The exhaust gas recirculation (EGR) valve introduces exhaust into the intake manifold to be burned in the combustion process, effectively lowering exhaust temperatures by diluting the air/fuel mixture. Because high exhaust temperatures generate nitrogen (NOx) emissions, the effect is lower levels of NOx. Production LS-series engines without an EGR valve perform an EGR function through the camshaft profile with valve timing that accomplishes a similar effect.

The EGR valves used with the Gen III PCM are unlike the early vacuum-operated EGR valves. The LT1 EGR valve (left) opens when vacuum is applied through the electrical solenoid. (Notice the vacuum lines from the solenoid to the engine and from the solenoid to the EGR valve assembly.) Newer engines use an electronically controlled EGR valve (right) with an internal sensor. Early engines being converted for Gen III PCM use either need a custom EGR solution or the elimination of the EGR valve.

Skip shift calibration options can be found in EFILive through Transmission Calibration > CARS/CAGS > Parameters.

The PCM supplies a 5V reference and ground to the EGR solenoid to open and close the valve through a PWM signal. EGR valve position is monitored by the PCM through a sensor within the EGR valve assembly. The PCM runs diagnostic tests to determine if the valve is operating as it is commanded.

AIR Pump Control

Secondary air injection (referred to as AIR, an acronym for “air injection reactor”) is a method of injecting fresh air into the exhaust stream. A similar method was implemented before electronic fuel injection as a means of lowering emissions through a more complete combustion of exhaust gases.

With the addition of the catalytic converter and modern PCM logic, the AIR system now serves the purpose of injecting fresh air into the exhaust steam during cold starts to effectively raise the exhaust temperatures at the catalytic converter, bringing the converter up to temperature faster for efficient burn of otherwise rich exhaust mixture. During normal engine operating temperatures, the AIR system continues to serve the purpose of reducing carbon monoxide (CO) and hydrocarbons (HC) emissions.

The electronic AIR pump is controlled by the PCM through a relay. The AIR pump relay coil and switch receive 12V battery power through a fused source. When the PCM applies a ground to the relay coil, the relay routes 12V to the AIR pump and fresh air is then introduced into the exhaust manifolds.

Skip Shift Solenoid Control

Vehicles with 6-speed manual transmissions (T56 transmissions) have a feature called skip shift (or computer-aided ratio selection, CARS). It improves fuel economy by using a PCM-controlled solenoid to block out second and third gear during certain driving conditions. The PCM applies a ground to this control circuit to energize the solenoid. An increase in throttle angle or vehicle speed is required to deactivate the solenoid. Many conversions disable this feature. Devices to eliminate skip shift are available, but a simpler solution is to disable the feature in the calibration.

If disabling skip shift (and/or reverse lockout), also be sure to disable DTC processing in the engine diagnostics section of the PCM calibration. By setting DTCs P0801, P0803, and P0804 to “Not Reported” within the processing enablers, the PCM ignores the processing of these DTCs.

Reverse-Inhibit Solenoid Control

Vehicles with 6-speed manual transmissions contain a reverse-inhibit (or reverse lockout) feature that prevents the driver from (accidentally) shifting into reverse when the vehicle is in motion. The PCM energizes the reverse-inhibit solenoid by applying a ground. With the solenoid energized, the driver can shift the transmission into reverse. When the PCM removes ground from the solenoid, the solenoid is deactivated and the driver is prevented from shifting into reverse.

If disabling skip shift (and/or reverse lockout), also be sure to disable MIL illumination in the engine diagnostics section of the PCM calibration. By setting DTCs P0801, P0803, and P0804 to “No MIL” within the MIL enablers, the PCM does not apply ground to the MIL control circuit (the MIL does not illuminate).

The Gen III PCMs are capable of controlling the skip shift and reverse-lockout solenoids found on the T56 6-speed manual transmission (Camaro, Firebird, and Corvette). PCM control of these solenoids can be enabled or disabled within the PCM calibration.

Transmission Control

All Gen III PCMs were used with 4L60-E transmissions. If your project includes a 4L60-E transmission, you can choose any Gen III PCM for 4L60-E control.) GM trucks and vans were the only vehicles to receive 4L80-E transmissions. Because the Gen III PCM was only used with 1999-newer trucks and vans, the 1997–1998 Gen III

PCM does not directly support 4L80-E transmissions. If your project includes a 4L80-E transmission, choose any 1999-newer Gen III PCM for 4L80-E control. (See Chapter 10 for more information on transmissions.)

Serial Data Output

Gen III PCMs have two Class 2 serial data outputs. In most production vehicles with a Gen III PCM, pin 58 of the PCM’s blue connector is used for Class 2 serial data communication. For conversions, this wire is used by the OBD-II DLC. (See Chapter 14 for more information about OBD-II.)

For use with electronic throttle systems only, the PCM has two discrete (meaning one source and one destination) universal asynchronous receiver-transmitter (UART) communication circuits for data transfer between the PCM and TAC module.(See Chapter 8 for more about electronic throttle systems.)

Written by Mike Noonan and Posted with Permission of CarTechBooks

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