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: Operation
The pick-up coil assembly consists of a permanent magnet, a pole piece and a pick-up coil. The coil assembly advances or retards ignition timing in response to the vacuum advance unit.
The timer core, mounted on the distributor shaft, rotates with the shaft inside the pole piece in the pick-up coil assembly. When the timer core external teeth align with the internal teeth of the pole piece, a voltage is induced in the pick-up coil. This voltage signals the electronic module to open the ignition coil primary circuit. See Fig 1 .
Current then decreases in the primary circuit, producing a high voltage in the ignition coil secondary circuit. This current travels from the coil, through the rotor, distributor cap contact and spark plug wires, and supplies the voltage required to fire the spark plugs.
The electronic module automatically controls dwell, extending it with increased engine speed. Dwell is not adjustable and periodic checks are unnecessary. The HEI system is able to ignite lean air/fuel mixtures due to its long spark duration.
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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.