Ignition System: Distributor

The Delco-Remy HEI-EST system consists of distributor housing, rotor, cap, 8-terminal ignition module, magnetic pick-up, pole piece, pick-up coil, connecting harness and the EST portion of the PCM. The distributor is connected to the EST system by a 4-wire connector leading to Powertrain Control Module (PCM).

No vacuum or centrifugal advance mechanisms are used. Based upon monitored input signals, PCM controls all spark timing changes. Most models are equipped with one or 2 knock sensors. Some models use an additional Electronic Spark Control (ESC) system, which retards timing in case of engine detonation (knock).

When the external teeth on the timing core approach, align with and pass the pick-up coil windings, an alternating current is produced in the pick-up coil windings. In the cranking mode, this alternating current signals switching transistors in the HEI module to make or break the ignition coil primary ground circuit. Once the engine starts, PCM takes control of primary ground circuit (EST mode).

When the primary ground circuit is removed, the magnetic field created by the flow of current in the primary windings collapses across the primary and secondary windings of the coil. This induces a high-voltage surge in the secondary windings of the coil. Secondary voltage is then discharged to the rotor, which distributes voltage to the appropriate spark plug terminal.