HEI Ignition Cap and Rotor

The purpose of the high energy ignition (HEI) cap and rotor are to provide a mounting location for the powerful HEI ignition coil, which typically produces 80,000 volts. The HEI cap and rotor are also designed to distribute this high voltage to the ignition wires while providing insulation so that the intense spark won't arc to any nearby ground point, thus causing a misfire. The ignition (or distributor) cap and rotor are housed in the vehicle's ignition system. As part of the ignition distributor, they allow each spark to be "distributed" from the ignition coil to the ignition wires and then to each spark plug.

When the engine is running, high voltage created by the ignition coil travels to the ignition cap and then through the coil terminal on to the ignition rotor. As the ignition rotor turns in the distributor, the rotor distributes the spark by sending it in a synchronized order through the spark plug wires to the spark plugs, located in each of the engine's cylinders.

Depending on the type of ignition system, the spark can range from 12,000 to 45,000 volts or even 80,000 volts in the case of an HEI ignition system. Due to the high voltage, it’s critical that the ignition system components are well-insulated. If insulation breaks down, the spark never arrives at the spark plug, causing the engine to run poorly—or not at all.

Be sure to inspect and/or replace the cap and rotor every 30,000 miles to avoid engine drivability problems.

Note: Engines utilizing multiple coil packs—also known as a coil-on-plug (COP) ignition—do not use an ignition distributor.

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