GM Corvette 1963-1982 Repair Guide

Breakerless Ignition Systems (Including H.E.I.)



Both the transistorized and H.E.I. systems operate in basically the same manner as the conventional ignition system, with the exception of the type of "switching device" used. As stated previously, the switching device of a conventional ignition system is the breaker point set. In the breakerless ignition systems, a toothed iron timer core is mounted on the distributor shaft. The timer core is mounted on the distributor shaft. The timer core rotates inside of an electronic pole piece. The pole piece has internal teeth (corresponding to those on the timer core) and contains a permanent magnet and pick-up coil (not to be confused with the ignition coil). The pole piece senses the magnetic field of the timer core teeth and sends a signal to the ignition module which electronically "calls the shots" concerning control of the primary coil voltage. The ignition coil operates in basically the same manner as a conventional ignition coil (though the ignition coils DO NOT interchange), but is controlled by the timer core, pole piece, and module; instead of the breaker points and condenser.

H.E.I. ignitions use a condenser, but it is primarily used for radio interference purposes.

As far as the mechanical advance is concerned, the operation is also basically the same as a conventional ignition system, with the exception that the timer core rotates on the distributor shaft instead of the distributor cam used in conventional systems. The vacuum advance unit moves the breaker plate in the same manner as the conventional system, but the timing changes according to the position of the pole piece instead of the breaker points.

Appearance wise, the transistorized ignition distributor looks very much like a conventional distributor, with the exception of a two-wire lead (with a quick-disconnect plug) coming from the distributor. Also, the transistorized system uses both an externally mounted ignition coil and an ignition amplifier unit which is finned for heat dissipation.

Do not use a conventional ignition coil in place of an electronic ignition coil, or vice-versa. Component damage could result.

The H.E.I. distributor looks nothing like a conventional distributor. The components of an H.E.I. distributor are all contained within the distributor (pole piece, ignition coil, module, etc.).

None of the electrical components used in either the transistorized or H.E.I. systems are adjustable. If a component is found to be defective, it must be replaced.


Before going on to troubleshooting, it might be a good idea to take note of the following precautions:

Timing Light Use

Inductive pick-up timing lights are the best kind to use if your car is equipped with HEI. Timing lights which connect between the spark plug and the spark plug wire occasionally (not always) give false readings.

Spark Plug Wires

The plug wires used with H.E.I. systems are of a different construction than conventional wires. When replacing them, make sure you get the correct wires, since conventional wires won't carry the voltage. Also, handle them carefully to avoid cracking or splitting them and never pierce them.

Tachometer Use

Not all tachometers will operate or indicate correctly when used on a H.E.I. system. While some tachometers may give a reading, this does not necessarily mean the reading is correct. In addition, some tachometers hook up differently from others. If you can't figure out whether or not your tachometer will work on your car, check with the tachometer manufacturer. Dwell readings, of course, have no significance at all.

H.E.I. System Testers

Instruments designed specifically for testing H.E.I. systems are available from several tool manufacturers. Some of these will even test the module itself. However, the tests given in the following information will require only an ohmmeter and a voltmeter.