The outlet of the transfer pump connects to a threaded restrictor known as the vent wire assembly. This component causes fuel under transfer pump pressure to undergo a pressure decrease. It also vents the pump of air and uses a wire with hooked ends to assist in this task.
The fuel passing through the vent wire assembly flows inside the pump housing to cool and lubricate most of the injection pump internal parts (refer to Figures 7-39 and 7-40). An outlet port in the governor cover allows fuel to enter the return system and travel back to the fuel tank.
The outlet port has a spring-loaded valve that regulates the flow of fuel from the injection pump housing into the return system. This valve, known as the housing pressure regulator, works with the vent wire assembly to provide a housing pressure of approximately 10 psi.
The vent wire assembly has several sizes, based on the amount of restriction required. The selection of this component is a part of the injection pump calibration procedure.
A solenoid in the governor cover uses a plunger to unseat the valve in the housing pressure regulator, causing housing pressure to drop to 0 psi. This component, known as the Housing Pressure Cold Advance (HPCA) solenoid, is ON during cold engine operation to cause a change in fuel injection timing. Refer to page 8-33 for information about the electrical circuit for the HPCA solenoid.
