Ignition System - Hall Effect: Operation

The computer has 2 functional modes, start and run. Start mode functions only during engine cranking and starting. Fixed amount of spark advance is provided, based on distributor position.

Run mode functions only when engine starts and is operating normally. Hall Effect pick-up assembly and 4 other sensors provide information to computer, which then varies spark advance to match engine operating conditions. Spark timing and dwell cannot be adjusted in start mode.

Engine sensors work together. If engine temperature drops below a predetermined temperature, coolant temperature switch signals the computer to prevent additional advance from the vacuum transducer signal. As temperatures rise, vacuum increases, and additional advance is called for.

For maximum advance, the carburetor switch must remain open. During the time when advance will not occur quickly, vacuum advance is controlled by engine RPM and will build up at a slow rate. If carburetor switch closes, this build-up of advance will be canceled.

Hall Effect pick-up signal is a reference signal, providing maximum amount of advance, based on sensor input. At the proper time, computer shuts off current to the ignition coil primary circuit. As the magnetic field collapses, a high voltage surge occurs in the secondary, firing the spark plugs.

If run mode of the computer fails, system will go into start mode. This enables the vehicle to be driven in for repair. However, performance and fuel economy will be poor. If the Hall Effect pick-up or start mode of the computer fails, engine will not start or run.