Spark Control Systems Diagnosis & Testing

Standard Cooling CTO:

COOLANT TEMPERATURE OVERRIDE (CTO) VALVE
1. Connect a suitable vacuum gauge to center port (port D) of CTO valve.
2. Manifold vacuum should be indicated on gauge when coolant temperature is below 155° F. Above this temperature, carburetor ported vacuum should be indicated. If defective, replace valve. Ported vacuum is only available when the throttle is opened to obtain an engine speed of approximately 1000 RPM.




FORWARD DELAY VALVE
1. Connect an external vacuum source to port on black side of valve.
2. Connect one end of a 24 inch length of rubber hose to vacuum gauge and opposite end to port on colored side of valve.
3. Apply a constant vacuum of 10 in. Hg and note the time required for gauge to move from 0 to 8 in. Hg. Compare the time to 4 +/- 0.8 seconds.
4. If defective, replace valve. If original valve is satisfactory, reinstall it with black side toward vacuum source.