Ignition Control Module: Description and Operation
Ignition Control Module And Coil Assembly:
18X & 3X Crank Sensors Pulses And Crankshaft Ref Signal Sent To PCM:
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. (The falling edge of each fuel control signal pulse occurs 70° before TDC of any cylinder.) The fuel control signal sent to the PCM by the ignition control module is an "ON-OFF" pulse occurring 3 times per crankshaft revolution. This is neither the 3X nor the 18X crank sensor pulse, but both of these are required before the ignition control module will generate the fuel control signal.
The ignition control module generates the fuel control signal by an internal "divide-by-6" circuit. This divider circuit divides the 1 8X crankshaft position sensor pulses by 6. The divider circuit is enabled, or ready to begin dividing, only after it receives a 3X crankshaft position sensor pulse. After beginning, the divider circuit does not need the 3X pulses to continue operating. If either the l8X or 3X pulses are missing at start-up, the divider will not generate a fuel control signal pulses (sent to the PCM), and no fuel injector pulses will occur.
^ Anytime the PCM does not apply 5 volts to the ignition control module "bypass" circuit, the ignition control module controls ignition by triggering each of the three coils in the proper sequence at a pre-determined dwell, with spark advance fixed at 10° BTDC. This is called module mode ignition. The ignition control module provides proper ignition coil sequencing during both the module and IC modes.
^ PCM applies 5 volts to the ignition module "bypass" circuit, signaling the module to allow the PCM to control the dwell and spark timing.
This is IC mode ignition. During IC mode, the PCM compensates for all driving conditions. Again, the ignition control module is responsible for proper ignition coil sequencing during both the module and IC modes.