The electronic ignition (EI) system is responsible for producing and controlling a high energy secondary 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 engine control module (ECM). The ECM 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 event. The EI system consists of the following components:

The crankshaft reluctor wheel is part of the crankshaft. The reluctor wheel consists of 58 teeth and a reference gap. Each tooth on the reluctor wheel is spaced at 6 degrees apart from each other, for a total of 60-tooth spacing around the circumference of the wheel. The crankshaft reluctor wheel is missing 2 of the 60 teeth. The 2 missing teeth are used to create 12 degrees of spacing, which is used for the reference or sync pulse. The sync pulse is used by the engine control module (ECM) to synchronize the coil firing with the crankshaft position, while the other teeth provide cylinder location during each crankshaft revolution.

The crankshaft position (CKP) sensor is a 3-wire sensor that provides a digital output signal. The wire circuits consist of an engine control module (ECM) supplied 5-volt reference circuit, a low reference circuit between the CKP sensor and the ECM, and an output signal circuit from the CKP sensor to the ECM. The CKP sensor detects magnetic flux changes of the teeth and slots of the 58-tooth reluctor on the crankshaft. The CKP sensor provides an ON/OFF DC voltage of varying frequency, with 58 output pulses per each crankshaft revolution. The frequency of the CKP sensor output signal depends on the speed of the crankshaft. The CKP sensor sends a digital square wave signal, which represents an image of the teeth on the reluctor wheel, to the ECM. The 12 degree reference gap on the reluctor wheel is used to identify crankshaft position. The CKP information, along with the camshaft position (CMP) sensor information is used to determine the correct time and sequence for fuel injection, ignition spark events, detect cylinder misfire, and the camshaft to crankshaft relative position.

The camshaft reluctor wheel is part of the camshaft gear. The reluctor wheel contains a pattern of 2 narrow teeth, and 2 wide teeth around the circumference of the wheel. The falling or trailing edges of the 4 teeth are evenly spaced at 90 degrees apart. The engine control module (ECM) recognizes the narrow and wide tooth patterns to identify camshaft position, or which cylinder is in compression, and which is in exhaust. The ECM also uses the reluctor wheel information to determine the camshaft relative position to the crankshaft position.

The camshaft position (CMP) sensor is a 3-wire sensor that provides a digital output signal. The wire circuits consist of an engine control module (ECM) supplied 5-volt reference circuit, a low reference circuit between the CMP sensor and the ECM, and an output signal circuit from the CMP sensor to the ECM. The CMP sensor detects magnetic flux changes between the teeth and slots on the 4-tooth reluctor wheel. The CMP sensor provides a digital ON/OFF DC voltage of varying frequency, with 4 varying width output pulses, per each camshaft revolution. The frequency of the CMP sensor output signal depends on the speed of the camshaft. The ECM will recognize the narrow and wide tooth patterns to identify camshaft position, or which cylinder is in compression and which is in exhaust. The information is then used to determine the correct time and sequence for fuel injection and ignition spark events. The ECM also uses the CMP sensor output signal to determine the camshaft relative position to the crankshaft position.

The knock sensor (KS) system enables the control module to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation, also known as spark knock. The KS system uses one or 2 flat response 2-wire sensors. The sensor uses piezo-electric crystal technology that produces an AC voltage signal of varying amplitude and frequency based on the engine vibration or noise level. The amplitude and frequency are dependant upon the level of knock that the KS detects. The control module receives the KS signal through the signal circuit. The KS ground is supplied by the control module through the low reference circuit.

The control module learns a minimum noise level, or background noise, at idle from the KS and uses calibrated values for the rest of the RPM range. The control module uses the minimum noise level to calculate a noise channel. A normal KS signal will ride within the noise channel. As engine speed and load change, the noise channel upper and lower parameters will change to accommodate the normal KS signal, keeping the signal within the channel. In order to determine which cylinders are knocking, the control module only uses KS signal information when each cylinder is near top dead center (TDC) of the firing stroke. If knock is present, the signal will range outside of the noise channel.

If the control module has determined that knock is present, it will retard the ignition timing to attempt to eliminate the knock. The control module will always try to work back to a zero compensation level, or no spark retard. An abnormal KS signal will stay outside of the noise channel or will not be present. KS diagnostics are calibrated to detect faults with the KS circuitry inside the control module, the KS wiring, or the KS voltage output. Some diagnostics are also calibrated to detect constant noise from an outside influence such as a loose/damaged component or excessive engine mechanical noise.

Each ignition coil has an ignition 1 voltage feed and a ground circuit. The engine control module (ECM) supplies a low reference and an ignition control (IC) circuit. Each ignition coil contains a solid state driver module. The ECM will command the IC circuit ON, which allows the current to flow through the primary coil windings for the appropriate time or dwell. When the ECM commands the IC 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 primary coils are current limited to prevent overloading if the IC circuit is held ON for an extended time. 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.

The engine control module (ECM) controls all ignition system functions, and constantly corrects the basic spark timing. The ECM monitors information from various sensor inputs that include the following:

There is one normal mode of operation, with the spark under engine control module (ECM) control. If the crankshaft position (CKP) pulses are lost, the engine will not run. The loss of a camshaft position (CMP) signal may result in a longer crank time, since the ECM cannot determine which stroke the pistons are on. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.