Computer Controlled Coil Ignition: Notes

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The Electronic Ignition (EI) system produces controls 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. Companion cylinders are a pair of cylinders that are at Top Dead Center (TDC) at the same time. The cylinder that is at TDC of the compression stroke is called the event cylinder. The cylinder that is at TDC of the cylinder 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 following components:

Crankshaft Position (CKP) sensors.
Camshaft Position (CMP) sensor.
Ignition Control Module (ICM) and ignition coils.
Powertrain Control Module (PCM).