Ignition System: Description and Operation

Ignition System:

The High Energy Ignition (HEI) system consists of the ignition coil, ignition module, distributor assembly (cap, rotor, magnetic pick-up, distributor shaft etc..), secondary wires, spark plugs, and the Electronic Spark Timing (EST) portion of the ECM. This system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time.

When the distributor shaft rotates, a square wave signal is generated by the hall-effect signal rotor. As a result a digital on-off DC current is supplied to the controller. When the voltage peaks, the controller sends a signal to the ignitor, and the ignitor breaks the circuit to ground from the negative (-) side of the primary winding. With the circuit broken, the magnetic field in the external ignition coil, which was generated by an electrical current passing through it, collapses. The high voltage induced by the collapsing field is then forced to find a ground through the secondary coil wire, the distributor cap, the rotor, the spark plug wires, and finally across the spark plug gap to the engine block.

All spark timing changes in the distributor are performed electronically by the ECM. The ECM monitors information from various engine sensors, computes the desired spark timing and signals the distributor to change the timing accordingly. No vacuum or mechanical advance mechanisms are used on this system.