GM Full-Size Trucks 1980-1987 Repair Guide

Electronic Spark Control (ESC) System (California or fuel injected only)



The Electronic Spark Control (ESC) operates in conjunction with the Electronic Spark Timing (EST) system and modifies (retards) the spark advance when detonation occurs. The retard mode is held for approximately 20 seconds after which the spark control will again revert to the Electronic Spark Timing (EST) system. There are three basic components of the Electronic Spark Control (ESC) system; the detonation sensor, distributor and the controller.

Should a Code 43 be set in the ECM memory, it would indicate that the ESC system retard signal has been sensed by the ECM for too long a period of time. When voltage at terminal L of the ECM is low, spark timing is retarded. Normal voltage in the non-retarded mode is approximately 7.5 volts or more.


The detonation sensor detects the presence (or absence) and intensity of the detonation (ping) by the vibration characteristics of the engine. The output is an electrical signal that goes to the controller. A sensor failure would allow no spark retard.


The distributor is an HEI/EST unit with an electronic module, modified so it can respond to the ESC controller signal. This command is delayed when detonation is occurring, thus providing the level of spark retard required. The amount of spark retard is a function of the degree of detonation.


The Electronic Spark Control (ESC) controller processes the sensor signal into a command signal to the distributor, to adjust the spark timing. The process is continuous, so that the presence of detonation is monitored and controlled. The controller is a hard wired signal processor and amplifier which operates from 6-16 volts.


Basic ignition timing is critical to the proper operation of the ESC system. Always follow the Vehicle Emission Control Information label procedures when adjusting ignition timing.

Some engines will incorporate a magnetic timing probe hole for use with special electronic timing equipment. Consult the manufacturer's instructions for the use of this electronic timing equipment.