If you don’t know how to “slew” a value in an EFI calibration — this chapter is for you. Here, you will be able to learn the basics of EFI and calibration, and how to take advantage of the advanced Gen III V-8 features like the built-in crank location sensor, cam sensor, and knock sensors. In fact, the Gen III V-8 engine, with its pushrod design and advanced sensors and controls, is perfectly suited to help bring the average automotive enthusiast into the next generation of modern hot-rod technology.
This Tech Tip is From the Full Book, HOW TO BUILD HIGH-PERFORMANCE CHEVY LS1/LS6 V-8S. For a comprehensive guide on this entire subject you can visit this link:
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In this chapter, we’ll discuss the operation, tuning, and debugging of both the GM factory EFI controller and aftermarket EFI controllers. You’ll see as much of the basics as is possible to show you in one chapter. Actually tuning the EFI calibrations isn’t fully documented here — that’s a book unto itself, and even that might not be enough to get you doing full “cal work” — as the pros call it. If you need to know more about EFI tuning, one such book to check out is the CarTech® title, Building and Tuning High-Performance Electronic Fuel Injection, by EFI101 guru Ben Strader. There is still plenty to talk about though, like defining EFI controls, exploring the common tables and values in the calibration, and discussing the many mistakes and successes you may encounter when setting up and calibrating your EFI engine.
In general, the EFI and calibrating business is an ever-changing landscape of technology. The calibration process requires short, careful steps to achieve a good tune-up. Taking small steps is a great way to avoid taking big steps backwards, which usually leads to broken parts and money being spent. Installing EFI systems and getting them calibrated is rewarding though, and it’s the future of performance vehicles. So read on to develop a foundation of info on this new high-performance world.
Slewing is the act of increasing or decreasing a specific value in one of the many lookup tables in the software program that controls an EFI system. Lookup tables are spreadsheets loaded with many values that the computer uses to determine the amount of fuel, spark, or one of the many other parameters to provide to the engine at a specific time to run it.
The EFI system works like this: the computer takes inputs from the many sensors that are on the engine and vehicle, then cross-references that data on the X and Y axis of lookup tables to find the correct amount of fuel or spark to apply at that specific moment. The computer applies the value located in the cell of the selected column and row, which usually represents an amount of voltage for a moment in time to act upon the engine. The ability of the computer to search through the lookup tables multiple times per second and then make adjustments on the fly is one of the advantages of an EFI system.
The most important actions the EFI system carries out include opening the fuel injector at a predetermined moment in the crank’s rotation for a specific amount of time, adjusting the spark advance, and engaging the idle air control (IAC) valve. The IAC is used to add more air to the engine as it is decelerating or warming up, like a high idle cam on carburetor linkage used to keep the engine from stalling.
As stated above, slewing means to tune the values in these tables. Calibrators will talk of slewing a specific value, an entire row, a large area of one of the tables, and sometimes an entire table. They’ll say, “Slew that up 2 or 3,” or, “I just slewed it a bunch as it was way too lean.” In other words, a value of 25 slewed up 2 units would leave the value at 27.
The changes are usually driven by data the computer is reading from the engine sensors, like the engine temperature. As an example, if an engine is up to temperature, but the calibration is telling the IAC to stay open, the engine will idle fast. To make a change, the values that are controlling the IAC relative to that temperature are slewed to get it to close a little more. The value in this case would usually represent the pulses going to the IAC step motor that moves the small plunger up and down in the bore of the IAC. The “open” pulses sent to the step motor would open the plunger in the bore, increasing the air being bled into the engine. “Close” pulses would leave the plunger further down in the bore, shutting air off to the engine and reducing the idle speed.
The controller is doing this type of adjusting all over the engine to optimize its power output, efficiency (mpg), driveability, emissions, and other desired parameters.
EFI Computer Contents
Port-injection EFI systems will usually consist of at least one electrically actuated fuel injector for each intake port, various sensors on the engine and vehicle, and a control module or computer. They’ll also have an electric fuel pump, fuel rails to attach the fuel line to the fuel injectors, a fuel pressure regulator, a wiring harness to tie everything together, and a throttle valve at the inlet to the engine. A Gen III V-8- equipped vehicle comes from GM with all these components.
The EFI system serves a variety of performance masters. For most automotive enthusiasts, EFI is used to attain the best possible air/fuel ratio and spark advance for the engine to produce the most power while operating at the best efficiency. Enthusiasts also enjoy the pleasant “start on the key” capability of the EFI system vs. the carburetor’s coldstart struggles. The EFI part-throttle control is also a welcome respite from the lean stumble often encountered with many carbureted cars.
For the OEMs like GM, they are looking for the best power and fuel economy with the lowest emissions, along with world-class driveability, durability, and NVH performance. It’s also important to attain low emissions of nitrous oxides (NOx), carbon dioxide (CO), and hydrocarbons (HC), as required by the Environmental Protection Agency (EPA) and its associate in controlling air pollution in the United States — the California Air Resources Board (CARB). GM has an impressive, federally certified emissions lab at its proving grounds in Milford, Michigan, to meet these ever increasing requirements for production vehicles. Changing to an aftermarket calibration on a production EFI GM vehicle that is licensed to be driven on public roads is not considered legal, unless the calibration has an Executive Order, or EO, from the CARB.
Aftermarket companies can apply for and, if they meet specified requirements, attain an EO for specific calibrations and hardware packages. The EO allows the aftermarket components and calibration to be street legal. Calibrations without an EO are for off road use only. This is done to control the amount of pollution being produced by road-going vehicles — whether they are stock production, or contain aftermarket components.
The computing power of the OEM and aftermarket controllers differs, but both are more than capable of creating smooth, powerful engines. The main differences are due to the complexity of the GM computer needed to control emissions, and more importantly, drive all the diagnostic codes. To give you an idea of the complexity, the calibration file in the GM controller is broken into eight large files for vehicles 1997 and up, each identified by a GM part number.
The programming inside the GM controller is larger because it needs to do much more than just control the engine operation. The GM controller contains OBD II, or onboard diagnostics version two, an EPA-mandated watchdog for the emission-controls on the vehicle. The GM computer is constantly logging values and adjusting the operation of the engine based on these values. This, along with a complex operating scheme, necessitates an abundance of computing power, which would explain the differences in capability of the GM and aftermarket controllers. In general, more computing power is good because it means better control of the engine is possible.
One good result of the OBD II system is very elaborate diagnostic software. This makes it easy for service shops to determine why a vehicle is not running correctly. They simply plug a reader into the diagnostic port and the vehicle will show them a numerical code that can tell them what’s wrong.
Now, enthusiasts that change the engine parts and/or the factory calibration will occasionally experience an SES, or “service engine soon” light, illuminating on the dashboard of their GM vehicle. The SES will light up for a plethora of reasons, but often it’s because the diagnostics software thinks a sensor reading is indicating that the pollution controls aren’t working properly. This doesn’t necessarily mean the engine is making more pollution than it did from the factory, but that the sensors and calibration think it’s dirtier. This is why modifying the factory calibration is important to getting an engine to run properly with a component combination different from what it came with from the factory.
Modern fuel injectors use an electrical current sent from the controller to stay open a short amount of time, usually a fraction of a second. The fuel injectors are all connected to a common fuel rail that contains pressurized fuel. When the injectors open, they allow pressurized fuel to spray into the intake port, mixing with the incoming air and entering the combustion chamber.
As an example, let’s look at a stock LS1 fuel injector, which is rated to flow 26.4 pounds per hour (lbs/hr) of fuel at 58.0 psi (4 bar) of fuel pressure. The more you learn about EFI, the more you’ll hear the lb/hr reference used often to denote the capability of an injector. The warning with this value is to know at what fuel pressure the lb/hr rating was measured at, as there are many different pressures used to rate fuel injector lb/hr flow. The two most common pressures are 43.5 psi (3 bar) and 58.0 (4 bar) psi.
Fuel injector capability is important to know because it needs to be matched with the power you intend to produce with your Gen III V-8. If you do change the fuel injectors, the fuel injector lb/hr calibration values will need to be changed so the computer will know the amount of fuel being let into the engine.
Mass Air, Speed-Density and Alpha-N
Mass air, speed-density, and alpha-N are three different types of EFI systems. These names refer to the type of sensor reading used by the controller to operate the engine. Mass air is the most complex, with many sensors to allow the system to constantly adjust to changing ambient, engine, and application conditions. Speed density uses the engine RPM and manifold pressure to select air/fuel ratios and timing advance. Alpha-N is little more than an electronic carburetor using rpm to decide how much fuel to add. Each of these systems has varying capability and is used for a variety of applications. Most production vehicles use the mass air and speed-density systems for their ability to adjust to multiple situations. Alpha-N systems are commonly used in racing applications where the engine will mostly be running at WOT (wide open throttle), and idle quality and part-throttle response aren’t really an issue.
The Gen III factory EFI is a mass-air system, so we’ll spend some time here explaining it. The mass-air system uses many sensors to understand what fuel, spark, and other parameters to apply to the engine. The critical sensor that reads the incoming air volume is the mass airflow (MAF) sensor. The engine inlet air rushes through this sensor, which contains at least one exposed wire. To measure the air rushing through it, the MAF passes an electrical current through the exposed wire. The voltage conducted through the wire drops at a rate proportional to the amount of air passing by and cooling the wire. The resulting value sent from the sensor to the controller is then compared to values in a calibration table to determine the amount of the air the computer believes is entering the engine.
Other sensors used for mass-air systems include a manifold air pressure (MAP) sender that reads the vacuum in the intake manifold, if it’s naturally aspirated. If the engine uses either a supercharger or turbocharger, the MAP will read positive pressure, too. Another sensor is needed to read the angle of the throttle blades, which obviously vary from closed to WOT. This sensor is called the throttle position sensor (TPS). Engine RPM also needs to be transmitted to the EFI controller. There are multiple ways to read RPM, but on past engines, it was usually off the ignition source, like the distributor. Obviously, the Gen III V-8 has no distributor, so it comes from the factory with an extremely accurate magnetoresistive-sensing crank trigger.
One of the most powerful sensors in an EFI system is the O2 sensor, because it’s used to adjust the air/fuel ratio. Located in the collector pipe of the exhaust manifold, the O2 sensor reads how much oxygen is left in the exhaust gases. Through scientific research done years ago, it is known that the optimum air/fuel ratio for complete combustion is 14.7:1, or 14.7 air molecules to 1 fuel molecule. The more oxygen in the exhaust, the leaner the engine is running (above 14.7), and thus, the more fuel is needed. An EFI system that is automatically adjusting to the input of the O2 sensor is operating in closed-loop mode. An EFI system that is operating without the input from an O2 sensor is in openloop mode. Advanced EFI systems will often operate in open loop when the engine is coming up to temperature and then switch to closed loop when everything is up to temp.
Sequential, Bank Fire and Batch Fire
Among the EFI systems listed above there is still more variety. The GM EFI system uses what is called a sequential-fire EFI system. The sequential system opens each fuel injector just before the intake valve opens. Bank-fire EFI systems open all the fuel injectors on each side of the engine at once and batch-fire EFI systems open all the fuel injectors to add fuel to each port all at once.
Sequential EFI requires eight solenoid (injector) drivers in the controller, while bank-fire EFI uses only four drivers (on a V-8). Sequential does show a little better power production overall than the bank or batch systems, but not much. Usually, sequential EFI is used because it allows better control of the fuel and spark for better emissions and low-rpm driveability.
Tuning the Gen III V-8 EFI
The Gen III V-8 might look like a simple engine design, but it is actually a very complex internal combustion engine designed to be operated precisely by electronic controls. The factory GM EFI controller reads input values from various sensors all over the vehicle, compares them to values on literally hundreds of lookup tables in the calibration, and selects the appropriate amount of fuel and timing advance to apply to each cylinder. This reading, comparing, and selecting of values happens multiple times a second, which is why the Gen III V-8 EFI system has such good manners, even with all of its power.
Gen III V-8 Engine Sensor Inputs
- Crank angle/Engine RPM
- Engine coolant temperature
- Oxygen sensors (in the exhaust)
- Oil temperature (on Corvette and some trucks)
- Air inlet temperature
- Throttle blade position
- Idle Air Control (IAC) location
- Manifold air pressure (MAP)
- Camshaft angle
- Knock sensors (to read detonation)
The factory GM EFI system and calibration have incredible capability, but this also makes tuning the controls for a modified engine combination a complex and often overwhelming task. Just to be clear, GM did not design the factory EFI system to be modified by consumers and does not offer any method for the public to do so. Various changes to the factory calibration can be made with equipment and software developed by automotive aftermarket companies. Some of these companies, like Hypertech, The Turbo Shop (TTS), JET, Diablo Sport, and LS1- Edit, have reverse engineered the GM code to allow automotive enthusiasts to access the electronic controls if they want more from their Gen III V-8.
The number of changes that can be made to the factory calibration varies depending on the aftermarket component being used. Most of the companies have simple, hand-held programmers that make changes based on menu-driven choices, but some of the more involved programming tools, like those available from Diablo Sport, TTS, and LS1-Edit, allow changes to just about any parameter you can imagine.
A lot of the aftermarket companies that sell products to alter the factory calibration, like Hypertech and DiabloSport, use handheld downloading pods. These handheld units are much more intuitive to operate than the fullblown calibration software programs. The pods use menu-driven questions with simple yes/no, true/false, or valuerequired questions that have value protections on them. This means you can’t make the transmission downshift into first when you go to WOT at 80 mph.
If you just want to make some finesse adjustments to your calibration, like gear ratio, tire size, and maybe add a little fuel here or there, these handhelds are a great solution.
Now, you might think the LS1-Edittype systems are for you, but please exercise caution before reprogramming your vehicle’s computer. To develop the original calibration, a team of GM engineers routinely spends at least 12 months or longer for each model of vehicle. Most calibrators have decades of experience doing what they do and have access to the finest diagnostic equipment on the planet. Each lookup table references many other tables as it makes minute decisions, multiple times per second. In other words, if you don’t know what you’re doing, get some guidance before making any changes!
There are many horror stories of enthusiasts scattering multiple engines, fragging control systems, and otherwise making a mess of a perfectly good car while attempting software changes without the proper knowledge. This isn’t meant to scare anyone, but just to clarify the complexity and consequences of the task. The best way to start learning is to start actually doing calibration work, but here are some general tips:
- Save a few copies of the original calibration in a safe place.
- Make small changes and test carefully, monitoring critical sensors to avoid damaging the powertrain.
- When in doubt, stop, seek knowledge, and demand clarity before making further changes to the calibration.
Don’t be the guy people talk about that confused transmission line pressure values with solenoid voltage, made a dramatic change to the calibration table, and blew the trans to smithereens on the next pass. Catastrophe is avoidable by simply stopping to ask for help.
The flip side of this discussion about avoiding damage is the rewarding experience of making hardware changes and being able to tune the calibration to take advantage of them. Simply put, the Gen III V-8 is one of the most impressive packages in how it positively reacts to power adding parts. As you saw early in this book, just bolting on a set of CNCported LS6 heads, an LS6 intake, and a performance cam boosted the power on a stock 345-hp LS1 (370 standard correction) to 450+ hp. That power increase wouldn’t have come without making a calibration change.
The following information refers to mainly one calibration system, LS1-Edit, but there are other companies providing software to make changes. LS1-Edit seems to be the most accepted by latemodel Gen III enthusiasts, and has a large number of features, which is why it was chosen here. While the software is called LS1-Edit, it works on all Gen III V- 8 engines powering Corvettes, Camaros, Firebirds, and full-size GM trucks. Even some sample web locations are included for your reference in the future.
The LS1-Edit software requires a laptop computer with the following capability:
- 200 Mhz Pentium or better
- 32 MB RAM • Windows 98, NT, XP, or 2000
- A free serial communications port (RS-232)
To get started, load the software into a laptop with the LS1-Edit CD. Then, the first step is to install the cable between the laptop and vehicle diagnostic port so the laptop can read the factory calibration. It’s best to read the factory software a few times to make sure the connection and system are robust enough for continuous communication. Having communication fail during software downloading could prove catastrophic for the calibration and controller.
Based on discussions with tuner shops and enthusiasts tuning GM Gen III V-8s, some of LS1-Edit’s easiest calibration changes include changing the tire size, speed limiter, engine redline, gear ratio, and fan on/off temperature. Also, some of the simpler spark tables can be changed very easily.
The medium difficulty changes include the shifting speed, shift firmness, and torque converter lockup for automatic transmissions. The most difficult values to tune are in the fuel tables for the engine and the torque management for the transmission.
If you plan on using a Gen III V-8 in a past model vehicle that isn’t emission controlled, like a street rod or muscle car, an aftermarket controller is often easier to hook up and tune for a specific application than the production controller and calibration. While there are some challenges getting up to speed on these stand-alone EFI systems, the rewards are simply amazing and completely worth the effort. What follows is an overview of the available systems, what it looks like to get an aftermarket controller system installed on a Gen III V-8, and some debugging tips and common pitfalls to avoid when creating a calibration.
The aftermarket controller business is still in its infancy, so there is really very little standardization (this is similar to the production vehicle controller business — as a tip, look for this business to become much more standardized in years to come). This newness is good in that a lot of innovation and specialization exists, but bad in that each system has a relatively steep learning curve.
One of the first stand-alone systems on the scene was ACCEL’s DFI EFI system. You can purchase everything you’ll need from ACCEL, including fuel injectors, the controller, and the fuel pump, making ACCEL a rare find in the aftermarket EFI business. There have been many recent revisions to the ACCEL system, resulting in their latest Gen VII system and software. Navigating within Gen VII is very intuitive, as is creating a custom calibration. The intuitive nature of the Gen VII software and the completeness of the ACCEL package make it a true plug-and-play system.
The systems from F.A.S.T. (which stands for Fuel Air Spark Technologies) are more representative of the component-level systems in the aftermarket EFI business today. The controller they sell was originally developed for Fel Pro, then sold to Federal Mogul, and is now available directly from F.A.S.T., which is a division of Comp Cams. This unit has been the benchmark for racers and performance enthusiasts because of the balance between its capability and cost. The MoTeC and Electromotive units probably have more raw capability, but they are considered more complex and costly than the ACCEL and F.A.S.T systems.Understanding your needs in an EFI system will help to get you the best controller for your money.
What Aftermarket EFI You Need
Most aftermarket EFI systems are speed-density systems, and there are more than enough sensors on the Gen III V-8 for the controller to run the engine.
Probably one of the more interesting aspects of the Gen III V-8 is how the engine speed is provided to the controller. The Gen III V-8 does not have a traditional distributor or a keyed harmonic balancer on the crankshaft. Instead, it has a 24x crank trigger mounted on the block.
This sensor wheel is mounted on the crankshaft inside and near the back of the engine. The production controller reads the steps on the dual-track crank wheel using a block-mounted crank sensor and compares those values with the readings from a camshaft sensor to determine which cylinder is firing at what time. As this book is being created, there are only a few aftermarket controllers that can read the factory crank- and cam-sensor outputs, but almost all of them are developing either adapters or complete systems to take advantage of the Gen III’s plug-and-play capability.
For those controllers that don’t have the capability to use the factory crank trigger, you’ll need to add a fourpoint trigger system. Aftermarket cranktrigger ignition systems, like those available from MSD, use trigger wheels with four small trigger magnets positioned at 90-degree increments on a wheel. A sensor reads the passing of each trigger magnet and the ignition controller uses this information to apply the correct spark to the engine. These aftermarket trigger wheels are usually installed on a Gen III V-8 either on the flywheel or in a wheel bolted to a harmonic balancer that is keyed to the crankshaft (usually by installing an aftermarket crank or having a keyway machined into the stock crank). But you probably won’t have to worry about adding a four-point crank trigger for long, because the factory crank wheel is far superior, so the aftermarket should catch up soon.
How to Limit Your Aftermarket EFI Frustration — Buy a Calibration!
Some common advice from enthusiasts that have installed aftermarket controllers is to beg, borrow, or buy an initial calibration. If you don’t get a calibration to start your engine with, the best way to begin is to just get the engine to run long enough to get it up to temp. All initial calibration tuning should be done only with everything up to temperature. So, if you have to run the engine at 2,000 rpm or higher to just get the temp in the package, then do it. Many aftermarket controller companies offer base calibrations or controllers that can create a calibration after the addition of your vehicle-specific information.
Written by Will Handzel and Posted with Permission of CarTechBooks