GM Blazer/Jimmy/Typhoon/Bravada 1983-1993 Repair Guide

Electronic Spark Timing (EST) System


Most of the vehicles covered by this guide utilize an electronic control system for all spark timing changes. Many of the HEI distributor equipped engines use the EST system instead of mechanical or vacuum advance mechanisms. The HEI (EST) spark control system make the ignition timing changes, necessary for emissions control, economy and performance. For more information on these systems, please refer to Engine Performance & Tune-up of this guide.