Reference Signal

Crankshaft Sensor Operation:

DESCRIPTION
The reference signal is a signal from the ignition control module to the ECM, and provides the ECM with engine position information. The ignition control module uses a magnetic crankshaft position sensor which protrudes into the block within less than 0.050 IN. of the crankshaft reluctor.
The reluctor is a special wheel cast on the crankshaft that has nine machined slots, eight of which are equally spaced (45 degrees apart). The ninth slot is spaced 8 degrees from one of the other slots. As the reluctor rotates with the crankshaft, the slots change the magnetic field of the sensor, causing an induced voltage pulse.

By counting the time between pulses, the ignition control module can recognize the pulse of the ninth slot (sync pulse). Based on this sync pulse, the module sends the reference signal to the ECM to calculate crankshaft position (used to fire coils in correct sequence) and engine speed.

The ECM utilizes the reference to determine spark timing and outputs the Ignition Control (IC) signal to the ignition control module.