System Operation

The Electronic Ignition (EI) system consists of the following:
^ Two ignition coils
^ The Ignition Control (IC) module
^ The Crankshaft Position (CKP) sensor
^ The Camshaft Position (CMP) sensor
^ The Powertrain Control (PCM) module

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 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 it's 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 engine load (manifold pressure or vacuum)
^ The engine coolant temperature
^ The intake air temperature
^ The crankshaft position
^ The engine speed (RPM)
^ The knock sensor
^ The TP sensor