Ignition System: Description and Operation

DESCRIPTION
The Electronic Ignition (EI) system does not use the conventional distributor and coil. This ignition system consists of two separate ignition coils, an electronic Ignition Control Module (ICM) and a Crankshaft Position (CKP) sensor, related connecting wires and the Ignition Control (IC) portion of the Powertrain Control Module (PCM) make up the remainder of the system.

OPERATION
A distributorless ignition system, such as this one, uses a "waste spark" method of spark distribution. Each cylinder is paired with the cylinder that is opposite it (1 - 4 or 2 - 3). The spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming up on the exhaust stroke.

The cylinder on the exhaust stroke requires very little of the available energy to fire the spark plug. The remaining energy will be used as required by the cylinder on the compression stroke. The same process is repeated when the cylinders reverse roles.

It is possible in a no load condition for one plug to fire even though the spark plug lead from the same coil is disconnected from the other spark plug. The disconnected spark plug lead acts as one plate of a capacitor, with the engine being the other plate. These two "capacitor plates" are charged as a current surge (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 still connected. Because of the direction of current flow in the primary winding and thus, in the secondary winding, one plug fires from the center electrode to the side electrode while the other fires from side electrode to center electrode.

This system utilizes the IC signal from the PCM, as does a distributor type ignition system equipped with IC, to control spark timing. To properly control ignition timing, the PCM relies on the following information:

^ Engine load (manifold pressure or vacuum).
^ Engine coolant temperature.
^ Intake air temperature.
^ Crankshaft position.
^ Engine speed (RPM).
^ Knock.
^ TP sensor.