General System Description
Ignition Control Wiring Diagram:
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 ECM 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, two hall-effect crankshaft position sensors, 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 ECM.
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 ECM, 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 on the compression stroke.
Crankshaft Position Sensor
3X Crankshaft Position Sensor - uses a concentric interrupter ring mounted to the rear of the crankshaft balancer has blades and windows that, with crankshaft rotation, either block the magnetic field or allow it to reach the "Hall-effect" switch.
The Hall-effect switch located closest to the crankshaft, is the 3X crankshaft position sensor. The interrupter ring has a special wheel cast on the crankshaft that has seven machined slots, six of which are equally spaced 60° apart. The seventh slot is 10° from one of the other slots.
As the ring rotates with the crankshaft, the slots change the magnetic field. This will cause the 3X "Hall-effect" switch to ground the 3X signal voltage supplied from the ignition control module. The ignition control module interprets the 3X "ON-OFF" signals as an indication of crankshaft position. The control module must receive the 3X signal to "fire" the correct ignition coil.
24X Crankshaft Position Sensor - uses the 24 evenly spaced blades and windows on the interrupter ring. The Hall-effect switch produces 24 "ON-OFF" pulses per crankshaft revolution.
The 24X crankshaft position sensor "Hall-effect" switch reacts the same as the 3X "Hall-effect" switch. The 24X signal is used for better resolution at a calibrated RPM.
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 3X crankshaft position sensor circuit.
^ It determines the correct ignition coil firing sequence, based on 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.
^ Sends a 3X crankshaft reference (fuel control) signal to the ECM. The ECM determines engine rpm from this signal. It is also used by the ECM to determine crankshaft position for Ignition Control (IC) spark advance calculations. The signal sent to the ECM by the ignition control module is an "ON-OFF" pulse occurring 3 times per crankshaft revolution.