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 Timing Advance
At engine speeds less than 400 RPM, ignition module controls spark advance by triggering coil(s) at a predetermined interval based on engine speed only. At engine speeds greater than 400 RPM (EST mode), ECM controls ignition timing.
ECM controls ignition timing based upon input signals from engine RPM reference line (ignition module), coolant temperature sensor, manifold air temperature sensor, throttle position sensor, knock sensor, vehicle speed sensor, gear position switch and MAP or MAF sensor.
The PROM portion of the ECM has a programmed spark advance curve based on engine speed. ECM calculates spark timing whenever an ignition pulse is present. Spark advance is controlled only when engine is running (not during cranking). ECM uses input signal values to modify PROM information, increasing or decreasing spark advance to achieve maximum performance with minimum emissions. To check ignition system operation, see BASIC TESTING or I - SYS/COMP TESTS article in this section.
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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.