Ignition System - V8: Description

The Delco-Remy High Energy Ignition system with Electronic Spark Timing (HEI-EST) is used on most General Motors vehicles equipped with gasoline engines. The 5.0L VIN 7 engine uses the Electronic Spark Control (ESC) system to retard spark timing when detonation occurs.

The Delco-Remy HEI-EST system, a part of all General Motors Computer Command Control systems, is designed to provide optimum performance through electronic control of air/fuel ratios, spark timing, air management and idle speed.

The distributor has neither vacuum nor centrifugal advance mechanisms. See Fig 1. The distributor contains a 7-terminal HEI-EST control module, a timer core, pick-up coil, radio noise suppression capacitor and, on most models, an integrally mounted ignition coil, located under the distributor cap's coil cover.

Fig 1: Disassembled View of HEI-EST Distributor Integral coil model shown.

The Hall Effect switch and shutter blades act as a second pick-up coil and timer core. When the engine is in the cranking mode, the pick-up coil and timer core are used to send RPM impulses to the ECM. When the engine is in the run mode, the Hall Effect switch and shutter blades perform this function. The number of shutter blades must equal the number of cylinders in the engine being used.

The distributor is connected to the EST system by means of a 4-wire connector, leading to the external electronic control module (ECM). The ECM (not the distributor HEI-EST module) receives voltage signals from a number of sensors. A typical system could be provided signals from oxygen, engine coolant temperature, throttle position, barometric pressure and manifold absolute pressure sensors, as well as the distributor pick-up coil and Hall Effect switch (if equipped).

CAUTION: Few components are interchangeable between HEI-EST and HEI distributors used on various engines. Be sure that the correct part is used, as similar appearance does not mean identical design or operation.

Fig 2: Schematic of HEI-EST Ignition System Includes Relationship to Computer Command Control ECM

There are 4 basic components to the ESC system: A detonation sensor, an HEI-EST distributor, an ESC controller, and the ECM. When detonation (engine knock) occurs, the detonation sensor sends an electrical signal to the ESC controller. The ESC controller amplifies this signal and transmits it to the ECM which then retards the spark timing until the ECM no longer receives a signal from the detonation sensor, through the ESC controller.

Fig 3: Schematic of Electronic Spark Control System