Computer Controlled Ignition

As the engine turns the distributor shaft, the shutter blades of the rotor/armature assembly pass through the Hall Effect sending unit's pick-up coil. A signal is then sent to the electronic control unit.

In addition to receiving engine speed information from the distributor, the electronic control unit receives engine load information from the intake manifold. Speed and vacuum signals are processed in the electronic control unit to control spark advance and dwell.

A throttle switch (located on the airflow meter) provides throttle information. Under normal conditions, the throttle position signal is sent to the electronic control unit.

The manifold vacuum signal is also processed by the control unit to control ignition timing. When the throttle is closed, (during deceleration and idle) the circuit is closed, and no signal is sent to the control unit.

The electronic control unit analyzes all information, and interrupts the signal to the ignition coil primary circuit. This causes a high voltage surge in the secondary circuit, firing the spark plugs at the proper time.

The knock sensor detects engine detonation. The electronic control unit receives a signal from the knock sensor during engine detonation and then retards timing. Timing is retarded 2° every 20 milliseconds until maximum retard of 6° is obtained, or detonation stops. Timing is then advanced in 1° increments every 20 milliseconds, until normal timing is achieved or detonation begins again.