HEI-Est Distributor

The Delco-Remy High Energy Ignition Electronic Spark Timing (HEI-EST) system consists of distributor housing, rotor, cap, 8-terminal ignition module, magnetic pick-up, pole piece, pick-up coil, harness with sealed connectors and the EST portion of the ECM. The distributor is connected to the EST system by means of a 4-wire connector, leading to Electronic Control Module (ECM).

On some models, the ignition coil is contained within the distributor cap, while other models have an externally mounted coil. A capacitor is installed in the distributor for radio noise suppression.

No vacuum or centrifugal advance mechanisms are used. All spark timing changes are controlled by the Electronic Control Module (ECM) based upon monitored input signals. Some models use an additional Electronic Spark Control (ESC) ignition retard system in the event 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 has started, ECM 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 it to the appropriate spark plug terminal.

On 4.9L, HEI-EST system is also equipped with a Hall Effect switch inside of the distributor. The Hall Effect switch produces a camshaft signal that is used by the ECM to determine the proper firing sequence for the injectors on the sequential fuel injection system. Loss of the camshaft signal will result in the fuel injection operating in a non-sequential mode and the setting of a related trouble code.