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.
Ignition System - HEI-Est: Operation: Sensors
The coolant temperature sensor advances spark on a cold engine and retards advance as the engine reaches normal operating temperature. If the engine is too hot, spark is retarded to prevent detonation. During light throttle operation, the throttle switch allows for additional advance.
Spark advance is also governed by input from coolant temperature, engine RPM, and Manifold Absolute Pressure (MAP) sensors. When MAP output voltage is low, ECM gives more advance. Less spark is given when MAP output voltage is high.
On engines with port fuel injection, the ECM will calculate spark advance using information from the Mass Air Flow (MAF) sensor, coolant temperature, and engine RPM. When the engine is under minimum load based on RPM and low air flow, more spark advance is given. When engine is under heavy load based on RPM and high air flow, less spark advance is given.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.
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