The Vortec V8 electronic ignition system is responsible for producing and controlling spark. This spark
is used to ignite the compressed air/fuel mixture at precisely the correct time. This provides optimal
performance, fuel economy, and control of exhaust emissions. This ignition system consists of a
separate ignition coil connected to each spark plug by a short secondary wire. The driver modules
within each coil assembly are commanded ON/OFF by the powertrain control module (PCM). The PCM
primarily uses engine speed and position information from the crankshaft and camshaft position (CMP)
sensors to control the sequence, dwell, and timing of the spark. The EI system consists of the following
Crankshaft Position (CKP) Sensor
The crankshaft position sensor is a three wire sensor based on the magneto resistive principle. A
magneto resistive sensor uses two magnetic pickups between a permanent magnet. As an element
such as a reluctor wheel passes the magnets the resulting change in the magnetic field is used by the
sensor electronics to produce a digital output pulse. The PCM supplies a 12-volt, low reference, and
signal circuit to the CKP sensor. The sensor returns a digital ON/OFF pulse 24 times per crankshaft
Crankshaft Reluctor Wheel
The crankshaft reluctor wheel is mounted on the rear of the crankshaft. The wheel is comprised of
four 90 degree segments. Each segment represents a pair of cylinders at TDC , and is further divided
into six 15 degree segments. Within each 15 degree segment is a notch of 1 of 2 different sizes. Each
90 degree segment has a unique pattern of notches. This is known as pulse width encoding. This
pulse width encoded pattern allows the PCM to quickly recognize which pair of cylinders are at top
dead center. The reluctor wheel is also a dual track-or mirror image-design. This means there is an
additional wheel pressed against the first, with a gap of equal size to each notch of the mating wheel.
When one sensing element of the CKP sensor is reading a notch, the other is reading a set of teeth.
The resulting signals are then converted into a digital square wave output by the circuitry within the
Camshaft Position (CMP) Sensor
The CMP sensor is also a magneto resistive sensor, with the same type of circuits as the CKP sensor.
The CMP sensor signal is a digital ON/OFF pulse, output once per revolution of the camshaft. The
CMP sensor information is used by the PCM to determine the position of the valve train relative to the
Camshaft Reluctor Wheel
The camshaft reluctor is either pressed onto the camshaft or part of the timing gear depending on the
application. The feature-or target- is read in a radial or axial fashion respectively. The wheel is a
smooth track, half of which is of a lower profile than the other half. This feature allows the CMP sensor
to supply a signal as soon as the key is turned ON, since the CMP sensor reads the track profile,
instead of a notch.
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Vortec V8 Truck Electronic Ignition system Description and Operation
Each ignition coil has an ignition 1 feed and a ground. The PCM supplies a low
reference and an ignition control (IC) circuit. Each ignition coil contains a solid state
driver module. The PCM will command the IC circuit ON, this allows the current to flow
through the primary coil windings for the appropriate time or dwell. When the PCM
commands the circuit OFF, this will interrupt current flow through the primary coil
windings. The magnetic field created by the primary coil windings will collapse across
the secondary coil windings, which induces a high voltage across the spark plug
electrodes. The coils are current limited to prevent overloading if the current is held
high too long. The spark plugs are connected to their respective coils by a short
secondary wire. The spark plugs are tipped with iridium for long life and efficiency.
Powertrain Control Module (PCM)
The PCM controls all ignition system functions, and constantly corrects the basic
spark timing. The PCM monitors information from various sensor inputs that include
• The throttle position (TPS) sensor
• The engine coolant temperature (ECT) sensor
• The mass air flow (MAF) sensor
• The intake air temperature (IAT) sensor
• The vehicle speed sensor (VSS)
• The transmission gear position or range information sensors
• The engine knock sensors (KS)
Modes of Operation
There is one normal mode of operation, with the spark under PCM control. If the CKP
pulses are lost the engine will not run. The loss of a CMP signal may result in a longer
crank time since the PCM cannot determine which stroke the pistons are on.
Diagnostic trouble codes are available to accurately diagnose the ignition system with
a scan tool.