GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual

ELECTRONIC SPARK CONTROL (ESC) SYSTEM

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Because varying octane levels in gasoline can cause detonation (spark knock) in any engine, some of the fuel injected engines covered by this manual which are equipped with HEI (EST) are also equipped with an Electronic Spark Control (ESC) system. The ESC is designed to detect detonation and retard spark timing up to 20° to reduce or eliminate detonation in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy.

 
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