ESC Detonation Retard Operation
In conjunction with the HEI-EST system, an Electronic Spark Control (ESC) retard system is used. System consists of a detonation (knock) sensor, a high energy ignition system, an ESC controller and PCM. On some models, the function of the ESC controller is built into the Memory Calibration (MEM-CAL) unit of the PCM.
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 PCM, depending upon application.
On vehicles using PCMs containing MEM-CAL units, the PCM 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 PCM. The voltage and frequency of this signal depend upon knock signals received by the sensor. The PCM 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. See appropriate I - SYS/COMP TESTS article in the ENGINE PERFORMANCE section below.