Signals, Interfaces and Shields

Wiring Diagram For EST Circuit:

PURPOSE

Electronic Spark Control (EST) is PCM or computer controlled ignition. Its purpose is to control the spark which ignites the air/fuel mixture at a calculated crankshaft position for each cylinder of the engine.

OPERATION

The ECM receives engine speed (RPM) from the HEI module, coolant temperature from the CTS, and Manifold Absolute Pressure from the MAP sensor. From this information the advance or retard of the spark is calculated. The EST line of the HEI (CKT 423) is used by the ECM to trigger the HEI module when the ECM is controlling spark timing.


LOCATION

The HEI module is located inside the HEI distributor and is serviceable separately.