Ignition System - HEI: Operation

The pick-up coil assembly consists of a permanent magnet, a pole piece, and a pick-up coil. The pick-up coil assembly is stationary, unless it is shifted by the vacuum control unit. The timer core position can also be shifted by the centrifugal weights.

The timer core, mounted on the distributor shaft, rotates with the shaft inside the pole piece portion of the pick-up coil assembly.

When the external teeth of the timer core line up with the internal teeth of the pole piece, a voltage is induced in the pick-up coil. This signals the electronic module inside the distributor, which opens the ignition coil primary circuit. See Fig 1.

The magnetic field in the ignition coil primary circuit collapses, inducing high voltage in the coil's secondary circuit. This travels through the distributor cap contact, rotor and secondary wires to fire the spark plugs.

The electronic module automatically controls dwell period, stretching it with increasing engine speed. Dwell is not adjustable, and periodic checks of dwell are unnecessary. The HEI system features a longer spark duration, which is desirable for firing lean and EGR diluted mixtures.