System Operation

The 2 functional modes of the Spark Control Computer are "Start" and "Run". The "Start" mode operates while cranking and starting only. The "Run" mode operates after the engine has started and during normal engine operation. The 2 modes never operate at the same time.

During cranking and starting the pick-up coil sends a signal to the computer which is in the "Start" mode. The "Run" mode is by-passed. During this time a fixed ignition advance is used. Advance is determined by distributor position (base timing).

The pick-up coil continues to send a signal to the computer after the engine starts. The computer is now in the "Run" mode and "Start" mode is by-passed. The amount of timing advance in the "Run" mode is controlled by the computer, based upon information received from the engine sensors.

Engine RPM and vacuum are the 2 factors determining ignition advance. When the ignition event occurs, depends upon computer programming. Advance from vacuum will be provided when the carburetor switch is open. The amount of advance is programmed into the computer and is proportional to the amount of vacuum and engine RPM.

Advance from an increase in RPM will be given by the computer when the carburetor switch is open and the computer is programmed to engine RPM. If there is a failure of the "Run" mode of the computer, the "Limp-In" mode will come into service and allow the vehicle to be driven in for repair. Performance and economy will be greatly reduced because of fixed and therefore retarded timing. If the "Start" mode or both pick-up coils fail, the vehicle will not start or run.