Ignition Control (IC) System Description
Ignition Circuit:
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 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 (EI) 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.
Camshaft Sensor
As the camshaft sprocket turns, a magnet in it activates the Hall-effect switch in the camshaft position sensor. When the Hall-effect switch is activated, it grounds the signal line to the PCM, pulling the cam signal line's applied voltage low. This is interpreted as a cam signal.
The cam signal is created as piston #1 is approximately 25° BTDC on the power stroke.
Crankshaft Sensor
The dual crankshaft position sensor contains two Hall-effect switches with one shared magnet mounted between them. The magnet and each Hall-effect switch are separated by an air gap.
The Hall-effect switch reacts like a solid state switch, grounding low current signal voltage when a magnetic field is present. When the magnetic field is shielded from the switch by a piece of steel placed in the air gap between the magnet and the switch, the signal voltage is not grounded. If the piece of steel (interrupter) is repeatedly moved in and out of the air gap, the signal voltage will appear to go "ON-OFF-ON-OFF-ON-OFF".
Compared to a conventional mechanical distributor, this "ON-OFF" signal is similar to the signal a set of breaker points in the distributor would generate as the distributor shaft turned and the points opened and closed.
Ignition Coils
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. Requiring less voltage to fire the plug on the exhaust stroke, most of the available voltage is sent to the compression stroke cylinder. This process is reversed as the cylinders' roles are reversed.
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 Ignition Control (IC) spark advance calculations.