Electronic Ignition System: Notes

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 uses one coil for each pair of cylinders. Each pair of cylinders that are at Top Dead Center (TDC) at the same time are known as companion cylinders. The cylinder that is at TDC of its compression stroke is called the event cylinder. The cylinder that is at TDC of its exhaust stroke is called the waste cylinder. When the coil is triggered both companion cylinder spark plugs fire at the same time, completing a series circuit. Because the lower pressure inside the waste cylinder offers very little resistance, the event cylinder uses most of the available voltage to produce a very high energy spark. This is known as waste spark ignition. The ignition coils and Ignition Control Module (ICM) are contained within one assembly. The ignition coil/ICM assembly is mounted in the center of the engine camshaft cover, with short boots connecting the coils to the spark plugs. The coil driver modules within the ICM are commanded ON/OFF by the Powertrain Control Module (PCM). The EI system consists of the following components:

1. Crankshaft Position Sensor  - See CRANKSHAFT SENSOR  under INPUT DEVICES.
2. Camshaft Position Sensor  - See CAMSHAFT POSITION SENSOR  under INPUT DEVICES.
3. Ignition Control Module and Ignition Coils  - Three dual tower ignition coils are mounted to the ICM, and are serviced individually. The ICM performs the following functions:
   • The ICM receives and processes the signals from the CKP sensor "B".
   • The ICM determines the correct direction of the crankshaft rotation, and cuts spark and fuel delivery to prevent damage from backfiring if reverse rotation is detected.
   • The ICM determines the correct coil triggering sequence, based on the 7X CKP signal. This coil sequencing occurs at start-up, and is remembered by the ICM. After the engine is running, the ICM will continue to trigger the coils in the correct sequence.
   • The ICM produces and inputs 3X reference signals to the PCM.
4. Powertrain Control Module  - See POWERTRAIN CONTROL MODULE  under COMPUTERIZED ENGINE CONTROLS.