Ignition Control Module: Description and Operation

PURPOSE
The Electronic Ignition system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time. To provide optimum engine performance, fuel economy, and control of exhaust emissions, the Powertrain Control Module (PCM) controls spark advance of the ignition system. Electronic ignition has several advantages over a mechanical distributor system.
^ No moving parts
^ Less maintenance
^ Remote mounting capability
^ No mechanical load on the engine
^ More coil cool down time between firing events
^ Elimination of mechanical timing adjustments
^ Increased available ignition coil saturation time

OPERATION
The electronic ignition system does not use the conventional distributor and coil. The ignition system consists of three ignition coils, an ignition control module, a dual hall-effect crankshaft position sensor, an engine crankshaft balancer with interrupter rings attached to the rear, related connecting wires, and the Ignition Control (IC) and fuel metering portion of the PCM.


Ignition Control Module
The ignition control module performs several functions:
^ It powers the dual crankshaft position sensor internal circuits.
^ It supplies the voltage signals that each respective Hall-effect switch pulses to ground to generate 3X and 18X crankshaft position sensor pulses.
^ Determines correct ignition coil firing sequence, based on how many 18X transitions occur during a 3X pulse. This coil sequencing occurs at start-up. After engine is running, the module remembers the sequence, and continues triggering the ignition coils in proper sequence.
^ Determines whether or not the crankshaft is rotating in the proper direction and cuts off fuel delivery and spark to prevent backfiring if reverse rotation is detected.
^ Sends a crankshaft reference signal to the PCM. The PCM determines engine rpm from this signal. It is also used by the PCM to determine crankshaft position for IC spark advance calculations.