System Operation

The computer has 2 functional modes: "Start" and "Run". "Start" mode functions only during engine cranking and starting. A fixed amount of spark advance is provided, based on distributor position. "Run" mode functions only when engine is running.

The amount of spark advance is determined by 3 factors: coolant temperature, engine speed, and manifold vacuum. The computer has a different advance schedule for a hot and a cold engine.

Timing advance is programmed into the computer. In a cold engine, advance depends only on amount of manifold vacuum. In a hot engine, advance depends on both manifold vacuum and engine speed. The advance curve is further modified by the carburetor switch. For maximum advance, carburetor switch must remain open.

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