ESC Detonation Retard Operation

In conjunction with the HEI-EST system, an Electronic Spark Control (ESC) retard system is used on some models. System consists of a detonation (knock) sensor (2 used on Corvette), a high energy ignition system, an ESC controller (some models) and the ECM. On some models, the function of the ESC controller is built into the Memory Calibration (MEM-CAL) unit of the ECM.

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

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

On vehicles using ECMs containing MEM-CAL units, the ECM supplies a 5-volt DC reference signal on the knock sensor signal line. Internal circuitry of the knock sensor will pull this voltage down to about 2.5 volts. When knock occurs, the knock sensor produces an AC voltage signal which rides on the 2.5-volt DC signal back to the ECM. The voltage and frequency of this signal depend upon knock signals received by the sensor. The ECM will retard spark timing until signals from detonation sensor cease.

A malfunction in the ESC circuit should set a related trouble code. If a code is not present and ESC system is suspected as the cause of driveability problems, perform functional check of ESC system. Refer to appropriate I - SYS/COMP TESTS article in this section.