ESC Detonation Retard Operation

Some models use an Electronic Spark Control (ESC) retard system along with the HEI-EST system. System consists of a knock (detonation) sensor, a high energy ignition system, an ESC controller (some models) and the PCM. On some models, the function of the ESC controller is built into the Memory Calibration (MEM-CAL) unit of the PCM.

When engine knock (detonation) occurs, knock sensor produces a low voltage AC signal. This signal goes to the ESC controller or directly to the MEM-CAL unit inside the PCM, depending upon application.

On models using an ESC controller, controller supplies the PCM with a 12-volt signal. When detonation occurs, controller grounds the 12-volt signal to the PCM, pulling the signal down to near zero volts. The PCM interprets this as a signal to retard timing. The PCM then retards spark timing until the ESC controller returns the 12-volt signal. If signal wire becomes open or grounded on models using ESC controller, PCM continuously provides full ignition timing retard.

A malfunction in the ESC circuit should set a related trouble code. If a code is not present and ESC system is suspected cause of driveability problems, perform functional check of ESC system. See SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE section.