System Description

EDIS 4 Dual Plug:

The Distributorless Ignition System (DIS) consists of a crankshaft mounted Dual Hall Sensor, Two 4 tower coil packs, and a ignition module.
The DIS eliminates the need for a distributor by using multiple ignition coils. Each coil fires two spark plugs at the same time. The plugs are paired so that one fires during the compression stroke while the other fires during the exhaust stroke. The next time the coil is fired the one that was on the compression stroke is now on the exhaust stroke and the one on exhaust is now compression. The spark in the exhaust stroke is wasted but little of the coil energy is lost. Two coils are mounted together in a coil pack. Each coil pack has two tach wires, one for each coil. Since there two plugs per cylinder, two coil packs are needed. One is called the Right Coil Pack (on the right side of the engine) the other the Left Coil Pack (on the left side of the engine). The Right Coil Pack and plugs operate continuously but the Left Coil Pack and plugs may be switched on or off by the EEC-IV processor. The processor computes the spark angle and the dwell for the ignition system.

Timing Diagram:

The Crankshaft Sensor is a dual digital output Hall device that responses to two rotating metallic shutters mounted together on the on the crankshaft. The PIP output is a 50% duty cycle signal that provides base spark timing. The CID output signal is also a 50% duty cycle and is needed so that the DIS module knows which coil to fire and for fuel timing in the EEC-IV processor. The CID Voltage (VBAT) is high on half of the cam revolution (180°) and low on the other half.
The EEC-IV processor determines spark angle using the PIP signal to set base timing. Spout is sent from the processor to the DIS module and serves two purposes: The leading edge fires the coil and the trailing edge controls the dwell time. This feature is called CCD or Computer Controlled Dwell.
The Ignition Diagnostic Monitor (IDM) is an output from the DIS module that provides diagnostic information concerning the ignition system to the EEC-IV processor for self-test.
Dual Plug Inhibit (DPI) allows the EEC-IV processor to switch the ignition system from the single to the dual plug operation. During cranking the vehicle is in the single plug mode (only the plugs on the right side of the engine fire). The EEC-IV processor sends a command to the DIS module to switch to the dual plug mode (both plugs in each cylinder are firing) when the engine has started.
If the CID circuit fails and an attempt to start the engine is made, the DIS module 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 EEC-IV failures that prevent the processor from providing spark angle or dwell commands. The processor opens the SPOUT line and the DIS module fires the coils directly from the PIP input. This results in a fixed spark angle of 10° and a fixed dwell.