GM Corvette 1963-1982 Repair Guide

Electronic Spark Timing (EST) System



The EST system is used on 1981-82 Corvettes. The ignition distributor of engines using the EST system does not have vacuum or mechanical spark advance mechanisms, as these functions are controlled electronically by the distributor module assembly and the ECM of the computer emissions system.

The purpose of the EST system is to precisely adjust the spark timing according to specific engine operating conditions, as sensed by the various monitoring devices of the computer emissions system.

The 1982 EST system is slightly different than the 1981 system, in that it uses a detonation sensor, mounted on the right side of the cylinder block in front of the starter. The purpose of the sensor is to "tell" the ECM when the engine begins to "ping," allowing the ECM to signal the distributor module to retard the spark timing just enough to keep the engine on the verge of detonation, without causing engine damage. If severe detonation occurs on engines equipped with the detonation sensor, the entire computer emissions system should be professionally tested.

Because both types of EST systems are directly tied into the computer emissions system, service, testing, and repair should be performed by a qualified, professional technician.