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 the 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 pickup plates located under cylinders No. 1 and No. 4 coil. 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.

DTC will set if the PCM voltage on cylinder No. 4 signal wire is not pulled to ground (CAM signal pulse) 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.