Ignition System: Description and Operation

GENERAL DESCRIPTION

The Computer Controlled Coil Ignition (C3I) system consists of a camshaft sensor, crankshaft position sensor, knock sensor, the Electronic Spark Timing (EST) portion of the PCM, an ignition module, three ignition coils, in a one piece unit called a coil pack, and the related connecting wires.

SENSORS

CAMSHAFT SENSOR
The camshaft sensor sends a signal to the PCM which uses it as a "sync pulse" to trigger the injectors in proper sequence. The cam signal is passed through the ignition module. It is not processed in any way.

CRANKSHAFT SENSOR
The crankshaft sensor sends a signal through the ignition module to the PCM. The PCM uses this reference signal to calculate engine speed and crankshaft position.

KNOCK SENSOR
The knock sensor detects detonation and signals the ESC module to retard the ignition timing. When the knocking stops, the PCM advances timing in small increments. This allows the PCM to maintain maximum timing advance under various conditions.

OPERATION
In much the same manner as the distributor type ignition system, this system uses the EST signal from the PCM. Above 450 rpm, the PCM applies 5.0 volts to the ignition module (bypass circuit) signaling the module to allow the PCM to control the dwell and spark timing. This is called EST mode. During EST mode, the PCM compensates for all driving conditions. In this mode, the PCM also monitors the knock sensor and retards the ignition timing if a knock is detected. When the knocking stops, the PCM advances timing in small increments.

Ignition Current Flow:

Three separate coils are mounted to the module assembly. Each coil provides the spark for two plugs simultaneously. Each coil can also be replaced separately. A "Waste Spark" method of distribution is used on this system. Each cylinder is paired with its opposing cylinder in firing order so that one cylinder on the compression stroke fires simultaneously with its opposing cylinder on the exhaust stroke. This process is reversed as the cylinders' roles are reversed.

The ignition module controls spark timing under 400 RPM and must receive a "sync-pulse" followed by a Crank Signal in that order to enable engine start up. The ignition module monitors the crankshaft sensor signals and based on these signals, sends a reference signal to the PCM to allow the correct spark and fuel injector control to be maintained during all driving conditions.