Ignition Timing: Adjustments

CIRCUIT DESCRIPTION
The electronic Ignition Control Module (ICM) sends a reference signal to the Powertrain Control Module (PCM) seven times per crankshaft revolution (7X reference) in order to indicate the crankshaft position and the RPM so that the PCM can determine when to pulse the ignition coils and control the ignition timing. The ICM applies 5 volts through the 7X reference circuit to the PCM. The PCM switches this circuit to ground for a very short period of time. The seventh pulse is the sync pulse and is used for crankshaft position reference.