Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1988S10/T10 BLAZER 4WD L4-151 2.5LREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSRELAYS AND MODULES - COMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULEDESCRIPTION AND OPERATIONMODES OF OPERATIONELECTRONIC SPARK TIMING (EST)
1988 Chevrolet S10/T10 Blazer 4WD L4-151 2.5L
Electronic Spark Timing (EST)
1988 Chevrolet S10/T10 Blazer 4WD L4-151 2.5LSECTION Electronic Spark Timing (EST)
The Electronic Spark Timing (EST) distributor contains no vacuum or centrifugal advance mechanisms. In addition to the connectors normally found on HEI distributors, the HEI-EST distributor also has four wires going to a four terminal connector. A reference pulse, indicating engine RPM and crankshaft position is sent to the ECM. The ECM determines the proper spark advance for the engine operating conditions and sends an "EST" pulse to the distributor.
In the case of EST failure, a back-up spark advance system is incorporated in the module.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.