Hall Effect Electronic Spark Control System: Operation

The computer has 2 functional modes, the start and run modes. The start mode functions only during engine cranking and starting. A fixed amount of spark advance is provided, based on distributor position. The run mode only functions when the engine starts and is operating normally. The Hall Effect pick-up assembly and the other 4 sensors provide information to the computer, which then varies spark advance to match engine operating conditions. Spark timing and dwell cannot be adjusted in the run mode.

Engine sensors work together. If engine temperature drops below a predetermined temperature, the 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 the carburetor switch closes, this build up of advance will be cancelled.

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

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