Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.