All pumps are equipped with a Housing Pressure Cold Advance solenoid. (Figure 4-67).
This component has been designed to allow more advance during engine warm-up. It consists of a solenoid assembly and a ball check return connector, both in a redesigned governor cover. The electrical signal which controls the operation of the solenoid is generated by a sensing unit mounted on the rear of the right cylinder head.
1984 and later H.P.C.A. is controlled by a cold advance circuit (C.A.C.) relay.
The switch is calibrated to open the circuit at 95°F for 83 and later (115° on 1982). Below the switching point, housing pressure is decreased from 8-12 psi to zero which advances the timing 3°. Above, the switch opens deenergizing the solenoid and the housing pressure is returned to 8-12 psi. The fast idle solenoid is energized by the same switch. The switch again closes when the temperature falls below 85°F (95°F on 1982).
PURPOSE:
1. Emission Control device.
2. Better cold starts.
3. Improves idle, reduces white smoke and noise when cold.
H.P.C.A. OPERATION
During cold warm-up conditions, the plunger moves up and the rod contacts the return connector ball. (Figure 4-68). When the ball is moved off of its seat, the housing pressure is reduced due to an increased flow through the connector. Because of lowered housing pressure, the resistance to the advance piston movement is less, and thus the piston can move further in the advance direction.
When the engine reaches normal operating temperature the electrical signal to the solenoid ceases, and the plunger is returned to its initial position. (Figure 4-69).
1984 H.P.C.A. Terminal will be changed (24669) because of 84 California System.
