Ignition System: OPTI-Spark

The PCM supplies and monitors two 5-volt reference signals to the Opti-Spark ignition module inside of the sealed distributor, one on high resolution signal line (360 pulses per camshaft revolution) and one on low resolution signal line (8 pulses per camshaft revolution). Ignition module will toggle these signals between zero and 5 volts as the camshaft turns. Camshaft-driven distributor is mounted behind water pump.

PCM uses these monitored reference signals in calculations used to control ignition timing. After computing necessary changes to ignition timing, PCM triggers ignition coil through the ignition coil driver. Unlike other type ignition systems, Opti-Spark does not use a by-pass circuit. Timing is always in EST mode.

By comparing the high and low resolution inputs, PCM can determine the position of cylinder No. 1 and TDC position. If either signal is missing, a code will set in PCM memory.