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

ELECTRONIC SPARK TIMING (EST) SYSTEM

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The High Energy Ignition (HEI) system controls fuel combustion by providing the spark to ignite the compressed air/fuel mixture in the combustion chamber at the correct time. To provide improved engine performance, fuel economy and control of the exhaust emissions, the ECM controls distributor spark advance (timing) using the Electronic Spark Timing (EST) system.

 
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