Discovery II
ENGINE MANAGEMENT SYSTEM - V8
DESCRIPTION AND OPERATION 18-2-71
Vacuum pump assembly
The vacuum pump assembly contains three components:
l
The vacuum pump.
l
The vacuum control valve.
l
The vacuum dump valve.
The vacuum pump provides the vacuum for the system while the two valves work in conjunction to allow the pump to
increase the vacuum to the pneumatic actuator (increase vehicle speed) or release vacuum from the pneumatic
actuator (decrease vehicle speed). On vehicles from 03 model year, the cruise control vacuum pump and pneumatic
actuator assembly is fitted with a heat shield to protect the components from heat from the exhaust manifold.
The vacuum control valve opens to allow the vacuum pump to increase the vacuum in the pneumatic actuator to
increase vehicle speed. When the vehicle reaches the set speed, the vacuum pump control valve closes to hold
vacuum in the pneumatic actuator and the vacuum pump is turned off by the cruise control ECU.
The vacuum dump valve is normally open. When cruise control is active, the cruise control ECU provides voltage to
close the vacuum dump valve. If power is lost, (e.g. when the brakes or clutch are applied or cruise control is turned
off at the cruise control master switch) the vacuum dump valve will immediately open and cruise control will be
deactivated.
The cruise control ECU provides power for all three components within the vacuum pump assembly. The cruise
control ECU provides earth control circuits for the vacuum pump and the vacuum control valve. The vacuum dump
valve is permanently grounded.
Input/Output
The cruise control ECU provides both power and earth to the components within the vacuum pump assembly. Current
draw at the vacuum pump assembly varies depending on components operating.
Vacuum pump current draw
When cruise is requested, the cruise control ECU provides voltage to the vacuum pump assembly and provides a
pulsed earth signal. The pulse period is dependent on the difference between the vehicle set speed and the actual
road speed. Removing the earth path switches off the pump.
Component
State of components
Vacuum dump valve
Off
On
On
On
Vacuum control valve
Off
Off
On
On
Vacuum pump
Off
Off
Off
On
Current draw, amperes
0
0.23
0.37
2.14
