DIS System Description
***THIS ARTICLE INCLUDES UPDATES MADE BY TSB #89-5A-13, DATED MARCH 1989***System Description
Figure 9 - 3.0L SEFI SHO and 3.8L SEFI SC Distributorless Ignition System (DIS):
The Distributorless Ignition System (DIS) (refer to Figure 9) consists of a crankshaft mounted Hall Profile Ignition Pickup (PIP) Sensor, a camshaft driven Hall Cylinder Identification (CID) sensor, a 6 tower DIS coil pack, and a DIS ignition module.
The DIS eliminates the distributor by using multiple ignition coils. Each coil fires two spark plugs at the same time. The plugs are paired so that as one fires during the compression cycle the other fires during the exhaust stroke. The next time the coil is fired the plug that was on exhaust will be on compression and the one that was on compression will be on exhaust (the spark in the exhaust cylinder 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 camshaft sensor is a Hall device that is mounted in the normal distributor location.
Figure 10 - 3.0L SEFI SHO and 3.8L SEFI SC DIS Waveforms:
The PIP output is a 50 percent duty cycle signal that provides base spark timing information. The CID signal output is also a 50 percent duty cycle signal and is required so that the DIS module knows which coil to fire and for fuel timing in the Electronic Engine Controller (EEC-IV) processor. CID is high (VBAT) half of the cam revolution (180 degrees) and low the other half (refer to Figure 10).
The EEC-IV processor determines spark angle using the PIP signal to establish base timing. Spout is sent from the EEC-IV 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 and is also the input signal for the vehicle tachometer. 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 system failures that prevent the EEC-IV processor from providing spark angle or dwell commands. The EEC-IV 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 degrees and fixed dwell.
Figure 12 - 3.8L SC DIS Component Location:
The DIS component locations are shown in Figure 12.