Ignition System: Description and Operation

ELECTRONIC IGNITION (EI)
The Electronic Ignition (EI) system does not use the conventional distributor and coil. This ignition system consists of 2 separate ignition coils, an electronic Ignition Control Module (ICM) and a Crankshaft Position (CKP) sensor. The related connecting wires and the Ignition Control (IC) portion of the PCM make up the remainder of the system.

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 of 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 available energy to fire the spark plug. The cylinder on the compression stroke uses the remaining energy as required. The same process repeats 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 a oscillating current across the gap of the spark plug still connected. Because of the direction of the 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 the side electrode to the center electrode.

This system utilizes the IC signal from the PCM, as does a distributor type ignition system equipped with IC, in order to control spark timing. 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