Ignition System: Description and Operation

GENERAL DESCRIPTION
The Computer Controlled Coil Ignition (C3I) system is a distributorless direct ignition system consisting of a 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.

ENGINE SENSORS
The PCM monitors a crankshaft position sensor on the engine and calculates the exact position of the crankshaft, for ignition timing control. A knock sensor detects detonation and signals the PCM to retard the ignition timing.

Ignition Current Flow:

Ignition Module/Coil Assembly Location And Firing Order:

IGNITION COILS
Three separate coils are mounted to the module assembly. Each coil provides the spark for two plugs simultaneously. Coils can also be replaced individually. 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.

IGNITION MODULE
The ignition module controls spark timing under 400 RPM. Below this engine speed, the timing is fixed at a factory preset value, for easy starting. The module must receive a "sync-pulse" from the camshaft sensor followed by a Crank Signal in that order to enable engine start up. At engine speeds greater than 400 rpm, the PCM controls ignition timing through signals to the module.

PCM - EST MODE
The module uses the EST signal from the PCM to determine spark timing. Above 450 rpm, the PCM applies a 5 volt reference signal to the by-pass circuit of the ignition module. While this voltage is present, the modules timing control is by-passed and the PCM controls timing and dwell (EST signal.) The module uses this EST signal to trigger the ignition coils in proper sequence and time. This is called EST mode. In this mode, the PCM also retards the ignition timing if a knock sensor signal is detected.