The Electronic Spark Control (ESC) system can be found on some 1981-83 vehicles along with most 1984 and later vehicles. The ESC system is a closed loop system that controls engine detonation by adjusting the spark timing. There are two basic components in this system, the controller and the sensor.
The controller processes the sensor signal and re-modifies the EST signal to the distributor in order to adjust the spark timing. The process is continuous so that the presence of detonation is monitored and controlled. The controller is not capable of memory storage.
The sensor is a magneto restrictive device, mounted in the engine block that detects the presence, or absence, and intensity of detonation according to the vibration characteristics of the engine. The output is an electrical signal which is sent to the controller.