DELCO-REMY Electronic Spark Timing (Est) Ignition System: Description

The Delco-Remy High Energy Ignition system with Electronic Spark Timing (HEI-EST) is used on all General Motors vehicles equipped with gasoline engines. The 4.1L VIN 4, 5.0L VIN 7 and 5.7L VIN 8 (Corvette) engines also use 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 1and Fig 2. 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. Distributors on vehicles equipped with 2.5L VIN 2 and 3.8L VIN K engines also contain a Hall Effect switch and shutter blades.

Fig 1: Disassembled View of EST Distributor (Model with Integral Coil Shown)

Courtesy of GENERAL MOTORS COMPANY

Fig 2: HEI-EST Distributor with Hall Effect Switch (External Coil Model Shown)

Courtesy of GENERAL MOTORS COMPANY

NOTE: On all models equipped with 4-cylinder engines, the ignition coil is mounted externally. On all other models, ignition coil is mounted on distributor cap.

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

On 2.5L VIN 2 engines, the shutter blades point upward since the ignition coil is mounted externally (not in the distributor cap). On 3.8L VIN K 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.

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 correct part is used, as similar appearance does not mean identical design or operation.

The HEI-EST module in the distributor has 7 terminals. The ignition coil battery terminal (positive) is connected to the "B" + or "B" terminal, the coil's "TACH" or negative terminal to the "C" terminal. See Fig 3. Terminals "N" and "P" are attached to the pick-up coil. HEI-EST module terminal "R" connects through the EST connector "B" to ECM terminal 10 (Distributor Reference Pulse Hi). Terminal "B" connects through terminal "C" to ECM terminal 11 (Ignition Module By-pass). Terminal "E" connects through connector "A" to ECM terminal 12 (EST). ECM terminal 13 (Distributor Reference Pulse Lo) connects to connector "D" and then to HEI-EST module ground.

Fig 3: Schematic of HEI-EST Ignition System Including Relationship To Computer Command Control Electronic Control Module

Courtesy of GENERAL MOTORS COMPANY

There are 4 basic components to the ESC system: A detonation sensor, and 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 advance until it no longer receives a signal from the detonation sensor, through the ESC controller.