Circuit Description

The Electronic Ignition (EI) module supplies a signal to the PCM whenever it determines that cylinder No. 4 fired on its compression stroke. Because of opposite coil tower polarity, the simultaneous firing of cylinders No. 1 and 4 are of opposite polarity as well. Under most conditions, the waste spark cylinder fires before the compression cylinder in sequence. The EI module can determine this polarity sequence and voltage amplitude by using capacitive pick-up plates located under cylinder No. 1 and 4 coils. If module senses a positive and negative sequence and high negative spike when cylinder No. 4 is on TDC, it pulls the PCM CAM signal to ground, signaling that cylinder No. 4 has just fired on compression. This signal, along with the double pulse received from the CKP sensor, synchronizes spark and fuel timing.

Only one cylinder No. 4 signal should be received every 20 crank pulses. DTC will set if CAM signal received at the PCM is incorrect or has too many pulses per crankshaft revolution when engine has been cranking for 5-10 seconds or when engine is running. Cam signal is continuously checked when crankshaft sensor pulses are received by the PCM, except under deceleration.