The electronic ignition (EI) system consists of the following:

In this system the secondary windings of each coil feed two spark plugs, and neither end of the windings are grounded. The engine cylinders are paired in opposites, i. e. cylinders 1 and 4, and 2 and 3. Each pair is on top dead center (TDC) at the same time. When a coil discharges both plugs fire at the same time to complete a series circuit. The cylinder on the compression stroke is said to be the event cylinder, the cylinder on the exhaust stroke the waste cylinder. The waste cylinder requires very little of the available energy to fire the spark plug, the event cylinder will use most of the energy. This same process will be repeated when the respective pair of cylinders are on the opposite stroke. This method of ignition is known as waste spark ignition.

It is possible in a waste spark ignition system for a spark plug to fire even if the spark plugs companion plug is disconnected. The disconnected plug wire acts as one plate of a capacitor, with the engine being the other plate. These two capacitor plates are charged as the spark jumps across the gap of the connected spark plug. The plates are then discharged as the secondary energy is dissipated in an oscillating current across the gap of the spark plug that is still connected. Secondary voltage requirements are very high with part of the circuit open, but the ignition coil has enough reserve energy to fire the connected plug at idle. Under high load it is possible neither plug will fire resulting in a severe misfire. In order to properly control the ignition timing, the PCM relies on the following information:

The Crankshaft Position (CKP) Sensor

This system uses a magnetic crankshaft position (CKP) sensor, mounted remotely from the ignition control module (ICM), which protrudes into the block within approximately 0.050 inches from the crankshaft reluctor. The graphic illustrates a typical sensor in relationship to the crankshaft reluctor. The reluctor is a special wheel which is cast into the crankshaft with 7 slots machined into the wheel, 6 of which are equally spaced (60 degrees apart). A seventh slot is spaced 10 degrees from one of the other slots and serves to generate sync-pules. As the reluctor rotates as part of the crankshaft, the slots change the magnetic field of the sensor, creating an induced voltage pulse. This signal is known as the 7x or low resolution signal because it occurs 7 times per crankshaft resolution. The powertrain control module (PCM) uses this signal to determine the speed and position of the crankshaft. The 7x reference signal is also used for fuel injector activation and ignition coil sequencing.

Ignition Coils

Two separate coils are mounted to the ignition coil assembly. Each coil provides the spark for two plugs simultaneously (waste spark distribution). Each coil can also be replaced separately.

Ignition Control Module (ICM)

The ICM receives the ignition control (IC) signals from the PCM which in turn triggers the corresponding ignition coils. Since the PCM controls spark timing and ignition control during crank and run, there is no bypass mode. The ICM is not repairable. When an ICM is replaced, transfer the remaining components to the new module.