Ignition System: Description and Operation

Electronic Spark Timing (EST) is part of the Computer Command Control System. The ECM monitors information from various sensors, computes the desirable spark timing and signals the distributor when timing changes are required. The distributor does not contain centrifugal advance weights, springs or a vacuum advance unit. Base timing is adjustable. If it is not correctly set, the entire spark advance curve will be off.

Spark knock (detonation) is controlled by an Electronic Spark Control (ESC) system that can retard ignition timing up to 20°. This allows the engine to use maximum spark advance to improve driveability and fuel economy.

The system consists of an ESC module and knock sensor. When the sensor detects knock, it produces a voltage signal that is sent to the ESC module. As long as the module receives no signal from the sensor, it sends a signal voltage (8-10V) to the ECM and the ECM calculates normal spark advance.

When the module receives a knock signal, it changes signal voltage to the ECM to 0V and the ECM retards timing to reduce knock.