Ignition Timing: Adjustments

Schematic:

CIRCUIT DESCRIPTION
The electronic Ignition Control Module (ICM) sends a reference signal to the Powertrain Control Module (PCM) seven times per crankshaft revolution to indicate crankshaft position and RPM so that the PCM can determine when to pulse the ignition coils and control the ignition timing. This signal is called medium resolution (7X reference) because it occurs seven times per crankshaft revolution. The ICM applies 5 volts through the 7X reference circuit and, in effect, 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 (CKP) reference.