Engine Speed Signal

HEI Wiring Diagram:

The engine speed signal comes from a seven terminal High Energy Ignition (HEI) module in the distributor along CKT 430 (DIST REF). Pulses from the distributor are sent to the PCM/ECM where the duration between these pulses are used to calculate engine speed. The PCM/ECM adjusts spark advance and sends a signal back to the distributor.