The High Energy Ignition (HEI) system, found on 1975-79 vehicles, is a pulse-triggered, transistor-controlled, inductive discharge ignition system which does not use contact breaker points. V8 distributors have all ignition components internally. Six-cylinder distributors have an externally-mounted ignition coil. The centrifugal and vacuum advance units are basically the same as those used to provide spark advance in breaker point distributors.
Engine ignition timing is adjusted the same as previous models, however observe the following items when working with HEI systems:
- Timing light connections should be made in parallel using an adapter at the distributor No. 1 terminal.
- Larger diameter (8 mm) spark plug wiring is used. Carefully twist the boots about a half turn in either direction to break the seal on the spark plugs.
- Connect dwell/tachometers to the "tach" terminal in the distributor cap connector and to ground. Some tachometers must connect from the "tach" terminal to the battery positive terminal. Follow the tachometer manufacturer's instructions.