Cold Start Solenoid (For Injection Pump): Description and Operation

The CAC circuit, used on California V8-379 diesel engines, advances injection pump timing approximately 4° during cold engine operation. The system includes an injection pump mounted cold advance solenoid, control relay and a temperature switch which is calibrated to open at temperatures above 95° F. In addition, operation of the fast idle solenoid is controlled by the CAC temperature switch and relay.
At temperatures below 95° F. the temperature switch is closed, battery voltage is applied to the control relay through the ignition switch and the relay energizes the CAC solenoid whenever the ignition is on with the engine stopped. When the engine is started a timer within the relay is activated by a signal from the alternator, and the timer allows the solenoid to remain energized for approximately 35 seconds. When the CAC solenoid is energized with the engine running, injection pump housing pressure is reduced from 10 psi to zero, effectively advancing injection timing. The fast idle solenoid, also controlled by the CAC relay, is not affected by the timer and remains energized as long as battery voltage is applied to the relay through the temperature switch.