System Description

Ignition System Schematic:

The Electronic Ignition (EI) system consists of a crankshaft mounted Hall sensor Profile Ignition Pick-up (PIP), a camshaft driven Camshaft Position (CMP) sensor, a 6 tower coil pack, and an Ignition Control Module (ICM).
The EI eliminates the distributor by using multiple ignition coils. Each coil fires two spark plugs at the same time. The plugs are paired so one fires during the compression cycle while the other fires during the exhaust stroke. The next time the coil is fired the plug that was on the exhaust stroke will now be on the compression stroke and visa versa. The spark that is used on the exhaust stroke is wasted but little of the coil energy is lost. Three coils are mounted together in a coil pack. The coil pack has three tach wires, one for each coil. The crankshaft sensor is a digital output Hall device (PIP) that responds to a rotating metallic vane mounted on the crankshaft damper assembly.
The CMP signal is also generated by a Hall device, mounted at the end of the rear camshaft. The vane cup has one tooth and is driven by the camshaft.

Timing Diagram:

The PIP output is a 50% duty cycle signal that provides base spark timing and fuel timing to the PCM. The CMP Battery Voltage (VBAT) is high on half of the cam revolution (180°) and low on the other half.
The PCM determines spark angle using the PIP signal to set base timing. Spout is sent from the processor to the ICM and serves two purposes: The leading edge fires the coil and the trailing edge controls the dwell time. This feature is called Computer Controlled Dwell (CCD).
The Ignition Diagnostic Monitor (IDM) is an output from the EI module that provides diagnostic information concerning the ignition system to the Powertrain Control Module (PCM) for self-test and is also the input signal for the vehicle tachometer. If the CMP circuit fails and an attempt to start the engine is made, the ICM will randomly select one of the three coils to fire. If hard starting results, turning the key off and then cranking again will result in another guess. Several attempts may be needed until the proper coil is selected allowing the vehicle to be started and driven until repairs can be made. The Failure Mode Effects Management (FMEM) system attempts to keep the vehicle driveable in spite of certain PCM failures that prevent the processor from providing spark angle or dwell commands. The PCM opens the SPOUT line and the ICM fires the coils directly from the PIP input. This results in a fixed spark angle of 10° and a fixed dwell.