Electronic Ignition System
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 the compression stroke is called the event cylinder. The cylinder that is at TDC of the 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 EI system consists of the Crankshaft Position (CKP) sensor, Camshaft Position (CMP) sensor, Ignition Control Module (ICM) and PCM.
- Camshaft Position Sensor
See CAMSHAFT POSITION SENSOR under INPUT DEVICES. - Crankshaft Position Sensor
CRANKSHAFT POSITION SENSOR under INPUT DEVICES. - Ignition Control Module & Ignition Coils
Three dual tower ignition coils are mounted to the Ignition Control Module (ICM) and are serviced individually. See Fig 1 . The ICM performs the following functions:- ICM receives and processes the signals from the CKP sensor "B".
- 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.
- 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 engine is running, ICM will continue to trigger the coils in the correct sequence.
- ICM produces and inputs 3X reference signals to PCM. The ICM contains the coil driver circuits that command the coils to operate.