The point type ignition system was used on the vehicles covered in this repair guide, until 1974. The Delco-Remy High Energy Ignition (HEI) System is a breakerless, pulse triggered, transistor controlled, inductive discharge ignition system available as an option in 1974 and as standard equipment after 1975.
There are only nine external electrical connections; the ignition switch feed wire, and the eight spark plug leads. On eight cylinder models through 1977, and all 1978 and later models, the ignition coil is located with the distributor cap, connecting directly to the rotor.
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 signal 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.
As already noted in Engine Performance & Tune-up , 1981 and later models continue to use the HEI distributor although it now incorporates on Electronic Spark Timing System (for more information on EST, please refer to Emission Controls ). With the new EST system, all spark timing changes are performed 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.