The Delco-Remy High Energy Ignition (HEI) System is a breakerless, pulse triggered, transistor controlled, inductive discharge ignition system.
The ignition coil is located with the distributor cap (except on the 1981 and later L4 engines, where it is a separate unit), connecting directly to the rotor. The major difference between the HEI System and the Unit Ignition System is that the HEI System is a full 12 volt system, while the Unit Ignition System incorporates a resistance wire to limit the voltage to the coil except during periods of starter motor operation.
The magnetic pick-up assembly located inside the distributor contains a permanent magnet, a pole piece with internal teeth, and a pick-up coil. When the teeth of the rotating timer core and pole piece align, an induced voltage in the pick-up coil signals the electronic module to open the coil primary circuit. As the primary current decreases, a high voltage is induced in the secondary windings of the ignition coil, directing a spark through the rotor and high voltage leads to fire the spark plugs. The dwell period is automatically controlled by the electronic module and is increased with increasing engine rpm. The HEI System features a longer spark duration which is instrumental in firing lean and EGR diluted fuel/air mixtures. The condenser (capacitor) located within the HEI distributor is provided for noise (static) suppression purposes only and is not a regularly replaced ignition system component.
1981 and later models continue to use the HEI distributor although it now incorporates an Electronic Spark Timing system (for more information on the EST, please refer to ). With the new EST system, all spark timing changes are performed electronically by the Electronic Control Module (ECM) which monitors information from various engine sensors, computes the desired spark timing and then signals the distributor to change the timing accordingly. Because all timing changes are controlled electronically, no vacuum or mechanical advance systems are used whatsoever.
The HEI distributor used on the 1981 and later V6 engine is, for the most part, identical to those used in 1980; the only discernible difference being the absence of a vacuum advance unit on its side. As noted previously, the distributor used on the L4 engine no longer utilizes an incorporated ignition coil and it too has no vacuum advance unit.