OBD-II compliance in 1996 brought a new ignition system to Vortec V-6 and Vortec V-8 engines. Engine position through a crankshaft sensor and reluctor wheel also meant improved ignition accuracy and misfire detection. Older HEI distributor ignition systems deliver spark and fuel based on distributor position. For these early systems, accuracy of spark and fuel delivery varies because the distributor gear must mesh with the camshaft and the camshaft must turn through the timing chain attached to the crankshaft sprocket. No doubt accuracy was close, but a signal from the crankshaft is the best way to determine the location of each piston. Ignition events based on crankshaft position means maximum horsepower and efficiency.
OBD-II compliance in 1996 brought a new ignition system to Vortec V-6 and Vortec V-8 engines. Engine position through a crankshaft sensor and reluctor wheel also meant improved ignition accuracy and misfire detection. Older HEI distributor ignition systems deliver spark and fuel based on distributor position. For these early systems, accuracy of spark and fuel delivery varies because the distributor gear must mesh with the camshaft and the camshaft must turn through the timing chain attached to the crankshaft sprocket. No doubt accuracy was close, but a signal from the crankshaft is the best way to determine the location of each piston. Ignition events based on crankshaft position means maximum horsepower and efficiency.
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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High-Resolution Crankshaft†Signal
GMís 24-pulse crankshaft signal is a series of long (12 degrees) and short (3 degrees) pulses that are 15 degrees apart. This 24x pattern is generated from a crankshaft reluctor mounted on an engineís crankshaft and through a CKP sensor. GMís 24x crankshaft reluctors feature two rows of teeth that are out of phase. This dual row pattern requires a CKP sensor capable of dual input and single output.
Early electronic fuel injection systems, such as on TBI and TPI engines, use an HEI distributor (left) with ignition module mounted to the base of the upper housing, within the cap. These early engines must rely on the distributor for setting base timing. The 1996-2002 Vortec V-6 and Vortec V-8 engines continue to use a distributor, but not for determining engine position. The Vortec distributor (right) is used to drive the oil pump, distribute spark, and provide the PCM with a camshaft position signal from the CMP sensor located within the cap.
The 24x crankshaft signal requires a 1x camshaft signal so the PCM can determine the stroke (intake or exhaust) of each piston based on its position during crankshaft rotation. Without a camshaft position signal, the PCM would have to guess between intake or exhaust stroke during engine startup.
The PCM supplies 12V high-reference and 0V low-reference signals to both crankshaft and camshaft sensors and receives back from each sensor a digital ON/OFF signal as each reluctor passes by its sensor.
24x Gen III
Although there are a variety of Gen III engines, every one has a crankshaft reluctor and sensor that produces a 24-pulse waveform (24x) used by the PCM to control spark and fuel events. This 24x signal represents crankshaft position. Because there are 720 degrees of crankshaft rotation to 360 degrees of camshaft rotation, a 1x signal from the camshaft allows the PCM to determine if a given piston is on the intake or exhaust stoke.
General Motors only used coil-per-cylinder ignition (eight ignition coils) with this 24x high-resolution crankshaft signal. Using the Gen III PCM with any other crankshaft signal does not allow for one coil for each cylinder. Unfortunately, the PCM calibration does not allow for remapping of the 24x encoded waveform to add or remove cylinders (ignition coils and injectors). However, if the engine firing order is mechanically changed, the PCM can be recalibrated for a new firing order.(See Chapter 7.)
All LS-series engines are equipped with eight ignition coils: four mounted to a bracket on each valve cover.
The Gen III crankshaft reluctor wheel is mounted on the rear of the crankshaft and within the engine block. The outer diameter of the crankshaft reluctor is exposed through a hole in the side of the block above the starter. The CKP sensor seals the sensor hole and returns a 24-pulse signal to the PCM while the crankshaft is turning.
Vehicles equipped with Gen III engines use a PCM calibration that requires this 24x crankshaft and 1x camshaft waveform relationship.
Identification of the crankshaft reluctor type (24x or 58x) is as easy as looking at the color of the CKP sensor mounted in the block above the starter. The black LS-series CKP sensor is used with a 24x crankshaft reluctor. What makes this sensor specific to the 24x reluctor is its ability to “read” a 24-pulse high/low signal (per 360 degrees crankshaft rotation) from the two rows of 24 teeth that are joined together, while out of phase, as one reluctor wheel.
The gray LS-series CKP sensor is used with a 58x crankshaft reluctor. This sensor is designed to “read” only one row of teeth from the crankshaft reluctor wheel. Where the 24x crankshaft reluctor is made up of two, out-of-phase rings, the 58x crankshaft reluctor contains only one row of 58 teeth. This gray CKP sensor is unable to properly produce a signal from GM’s 24x crankshaft reluctor.
Gen III engines have a CMP sensor located at the rear of the engine where you commonly see a distributor for small-block Chevy engines. This CMP sensor gets its signal from a machined ring toward the rear of the camshaft. This sensor/reluctor pair generates a near 50-percent duty-cycle (on/off) high/low signal so the PCM can determine the stroke (intake or exhaust) for any given cylinder.
Gen IV engines mount the CMP sensor in the front timing cover and get a signal from the face of the camshaft timing sprocket. Early Gen IV engines are equipped with a 24x crankshaft reluctor and 1x camshaft reluctor. These engines use the same CMP sensor and timing cover as the later engines equipped with a 58x crankshaft reluctor and 4x camshaft reluctor. The CMP sensor output (1x or 4x) is determined by the signal surface area of the camshaft timing sprocket.
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/crankshaft-camshaft-signals-guide/
EFI Connection’s 24x crankshaft reluctor design has a dual row of teeth and requires the use of a dual-input, single-output sensor. This reluctor installs in front of the crankshaft timing sprocket and is held firmly in place with the tightening of the crankshaft balancer bolt. The crankshaft signal solution requires a timing cover with provision for a CKP sensor.
EFI Connection’s 24x LT1 conversion kit includes a crankshaft reluctor, crankshaft sensor, camshaft reluctor, camshaft sensor, and camshaft sensor housing. The camshaft sensor housing is installed on the face of the timing cover where the Optispark distributor used to reside. A 1996-1997 LT1 timing cover is required.
Due to the crankshaft seal area of the GM LT1 timing cover, a crankshaft reluctor and double-row timing set cannot be used with a GM LT1 timing cover. TPIS manufactures several anodized billet-aluminum timing cover solutions for use with EFI Connection’s 24x small-block/LT1 crankshaft reluctor. The TPIS billet-aluminum timing covers are available with or without provision for the upper water pump driveshaft. A big-block Chevy diameter crank seal is also an option for engines requiring a larger-diameter crankshaft hub or balancer.
Identifying a Gen III engine is easy; simply look at the color of the crankshaft position sensor above the starter. All engines equipped with a Gen III 24x reluctor use a black crankshaft position sensor; all engines equipped with a Gen IV 58x reluctor use a gray crankshaft position sensor.
All Gen III engines have a camshaft position sensor in the rear of the engine behind the intake manifold. All Gen IV 24x and 58x engines have a camshaft position sensor in the front timing cover. Gen IV 24x engines use an E40 ECM and can be found in the 2005 Corvette, 2005-2006 GTO, 2005-2006 Trailblazer, and 2005-2006 SSR. (This book does not cover Gen IV engines and electronics.)
EFI Connection 24x System
To introduce the LS-series coil-per-cylinder ignition system with Gen III PCM control to the Gen I small-block Chevy engine, EFI Connection designed a smaller diameter 24x crankshaft reluctor that installs within the 1996-2002 Vortec engine timing cover and uses a GM crankshaft position sensor. General Motors had already provided the required 1x camshaft signal through the 1996-2002 Vortec distributor, but EFI Connection’s cast-aluminum distributor cap eliminates any spark plug wire provision on the distributor; it’s function is to produce a camshaft position signal and drive the oil pump. The 24x crankshaft signal components and 1x camshaft signal components make the Gen I small-block Chevy engine ready for Gen III PCM control.
EFI Connection eliminated the problematic Optispark distributor used with all Gen II LT1 and LT4 engines by using the same 24x small-block reluctor and a 1996-1997 LT1 timing cover. The 1x camshaft position signal is achieved through EFI Connection’s LT1 camshaft reluctor installed in front of the camshaft timing sprocket and the Gen IV camshaft position sensor installed in EFI Connection’s cast-aluminum cam sensor housing. These LT1 camshaft signal components are installed in place of the Optispark distributor. The 24x crankshaft signal components and 1x camshaft signal components make the Gen II LT1 and LT4 engines ready for Gen III PCM control.
With the 24x crankshaft signal and the 1x camshaft signal, the Gen III PCM controls early V-8 engines just as it controls a Gen III engine. PCM calibration file selection requires a base calibration from a Gen III vehicle. This is significant because it allows for any LS-series vehicle hardware option (throttle type, transmission type, and so on). Tuners can choose from any Gen III base calibration file. Correcting the firing order requires the engine wire harness reassignment of injectors and coils 2 and 3 and 4 and 7. In addition, the PCM requires a calibration update of the injector bank assignments table for proper fuel delivery (see 8-4 and 8-5 Chapter 7 for more details). The tuner works with this PCM just as he would with any LS-series engine.
Low-Resolution Crankshaft Signal
The Gen III PCM (GM# 12200411) was also used with the 2001-2002 Gen I small-block and Vortec V-6 engines. While these engines are fitted with a low-resolution crankshaft signal, the crankshaft sensor principle is the same: a digital ON/OFF signal represents crankshaft location. General Motors never released a coil-per-cylinder ignition system that used a low-resolution crankshaft signal, meaning that the PCM cannot be recalibrated for coil-per-cylinder ignition with a low-resolution crankshaft signal. In addition, because General Motors did not use an electronic, drive-by-wire throttle system, only a cable throttle body is supported.
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All 1996-2002 Gen I small-block engines found in production vehicles use a 4x crankshaft reluctor. This reluctor is installed on the crankshaft in the front timing chain cover. Combined with a CKP sensor, the PCM uses the signal to determine engine position.
All 1996-2006 4.3L V-6 engines found in production vehicles use a 3x crankshaft reluctor. This reluctor is installed on the crankshaft in the front timing chain cover. Combined with a CKP sensor, the PCM uses the signal to determine engine position.
The PCM monitors the relationship of the crankshaft to the camshaft through a CKP sensor and a CMP sensor. The sensors return digital ON/OFF signals to represent engine position. This waveform is a visual representation of two complete revolutions of the crankshaft.
Gen I Vortec V-8
Since 1996, the Gen I small-block Vortec engines are equipped with a low-resolution 4x crankshaft signal and a 1x camshaft signal. This means all Gen I small-block Chevy engines are easily converted to PCM use (GM# 12200411) with the addition of a GM 4x crankshaft reluctor, CKP sensor, timing cover, and Vortec distributor. The 4x crankshaft signal is used by the PCM to identify piston pairs at top dead center (TDC). Combined with the 1x camshaft signal from within the Vortec distributor, the PCM determines the stroke for any given piston. Only single coil and distributor ignition are possible for an engine equipped with a low-resolution 4x crankshaft signal.
Vortec V-6
Since 1996, Vortec V-6 engines have been equipped with a low-resolution 3x crankshaft signal and a 1x camshaft signal. This means all early 4.3L V-6 Chevy engines are easily converted to PCM use (GM# 12200411) with the addition of a GM 3x crankshaft reluctor, CKP sensor, Gen I small-block Vortec timing cover, and Vortec distributor. The 3x crankshaft signal is used by the PCM to identify piston pairs at TDC. Combined with the 1x camshaft signal from within the Vortec distributor, the PCM can determine the stroke for any given piston. Only single coil and distributor ignition are possible for an engine equipped with a low-resolution 3x crankshaft signal.
The PCM monitors the relationship of the crankshaft to the camshaft through a CKP sensor and a CMP sensor. The sensors return digital ON/OFF signals to represent engine position. This waveform is a visual representation of two complete revolutions of the crankshaft.
Written by Mike Noonan and Posted with Permission of CarTechBooks
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