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.
Distributor Modulator: Operation
Current is supplied to the control module when the ignition is turned on. The current then triggers the solenoid valve inside the control module to shut off carburetor vacuum to the distributor vacuum advance unit. As vehicle speed increases, the speed sensor, in line with the speedometer cable, builds up a voltage frequency proportional to vehicle speed. This voltage is sent to the amplifier inside the control module. The solenoid valve is then triggered and it opens, allowing vacuum advance at about 23 miles per hour. As the vehicle decelerates and the speed drops to about 18 miles per hour, the reduced voltage from the speed sensor causes the solenoid to close. Now no vacuum is applied to the distributor vacuum advance unit.
Use the Manual With the Right Hardware
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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.
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