Ignition System - HEI-Est: Description

The Delco-Remy High Energy Ignition system with Electronic Spark Timing (HEI-EST) is a part of all General Motors Computer Command Control (CCC) systems. The CCC is designed to provide optimum performance through electronic control of air/fuel ratios, spark timing, air management, and idle speed. The 3.0L VIN A, 3.8L VIN A, 4.1L VIN E, and 5.0L VIN G engines also use the Electronic Spark Control (ESC) system to retard spark timing when detonation occurs.

The distributor has neither vacuum nor centrifugal advance mechanisms. See Fig 1 and Fig 2. The distributor contains a 7-terminal HEI-EST control module, a timer core, pick-up coil, and radio noise suppression capacitor.

Fig 1: Disassembled View of HEI-EST Dist (Integral Coil Model Shown)

Fig 2: HEI-EST Dist W/ Hall Effect Sw. (External Coil Model Shown)

All spark timing changes in the distributor are controlled by the 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).

Distributors on some vehicles equipped with 4 or 6-cylinder engines contain a Hall Effect switch and shutter blades. 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.

On 4-cylinder engines, the shutter blades point upward since the ignition coil is mounted externally (not in the distributor cap). On 6-cylinder engines, the shutter blades point downward to provide space for the distributor cap mounted (integral) ignition coil. The number of shutter blades must equal the number of cylinders in the engine being used.

Fig 3: 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. The ECM will then retard spark timing until the ECM no longer receives a signal from the detonation sensor.

Fig 4: Schematic of Electronic Spark Control System