This ignition system was standard for vehicles equipped with the 3.0L engine in 1988-89. The system is similar to the SMEC system in operation except that it uses a different type of distributor. The computer receives its input from an optical distributor. The signals are used to control fuel injection, ignition timing and engine idle speed.
The timing member in the distributor is a thin disk, driven at half the speed of the engine, from the left camshaft. The disk has 2 sets of slots in it. The outer, high data rate slots, occur at 2 degrees of engine rotation. They are used for ignition timing at engine speed of up to 1200 rpm.
The inner, or low data rate set, contains 6 slots which are correlated to TDC of each cylinder. This is used to trigger the fuel injection system. This data set functions at engine speed over 1200 rpm. This set also controls the ignition timing.
Light emitting diodes and photo sensors are mounted in facing positions on opposite sides of the disk in the distributor. Masks over the LED's and the diodes focus the light beams onto the photo diodes. As each slot passes between the diodes, the light beam is turned on and off. This creates an alternating voltage in each photo diode, which is converted into on/off pulses by an integrated circuit within the distributor.
The distributor also delivers firing pulses from the coil to each of the cylinders through the cap and rotor.