Primary LP Fuel Pump (Fuel delivery system - Td4)

The ECM controls the opening and closing of the valve using PWM signals to control the solenoid. When the solenoid is de-energised, the valve is open and fuel pressure is diverted into the fuel return line. When the solenoid is energised the valve is closed allowing the fuel pressure to rise. The ECM controls the fuel pressure by adjusting the duty cycle of the solenoid via the PWM signals.

The ECM determines the required fuel pressure by monitoring signals corresponding to the following parameters: l Engine load l Accelerator pedal position l Fuel rail pressure l Engine speed l Engine temperature.

If the pressure control valve fails the engine may not start, power loss may occur and the engine will stall.

Primary LP Fuel Pump

The primary low pressure pump is located in an aperture in the top face of the fuel tank. The pump is sealed in the tank with a rubber seal and secured with a locking ring, which requires a special tool for fitment and removal. Access to the pump is via an access panel located below the RH rear seat.

An electrical connector on the top of the pump supplies power and ground connections for the pump and the fuel gauge potentiometer. The pump receives a power supply from the fuel pump relay.

The pump is submerged in the fuel and draws fuel from an integral swirl pot which maintains a constant fuel level around the pick-up. The swirl pot also mixes warm fuel returning to the tank with the cool fuel in the tank. The pump is capable of a maximum output of 165 litres/hour at a pressure of 2.0 bar (29 lbf/in²) and a power supply of 11.5V.

A float operated potentiometer is also located on the pump and provides a variable resistance to earth for an output from the fuel gauge in the instrument pack. The potentiometer float moves with the fuel level in the tank and the resultant resistance is interpreted by the gauge for the level of remaining fuel.

The pump has a connection for a fuel supply to the fuel burning heater pump, located in the RH wheel arch, on vehicles fitted with this option. For further details refer to Heating and Ventilation. HEATING AND VENTILATION, DESCRIPTION AND OPERATION, Description.

Secondary LP Fuel Pump

The secondary low pressure pump is located in a plastic housing, adjacent to the fuel filter, in the engine compartment on the LH inner wing.

The pump is a secondary in-line screw pump designed to aid fuel flow through the filter in cold conditions. The pump is capable of a maximum output of 210 litres/hour at a pressure of 1.8 bar (26 lbf/in²) and a power supply of 12V.

The pump has a fuel input pipe connection at the bottom and a fuel output pipe connection to the filter at the top. An electrical connector on the top of the pump supplies power and ground connections for the pump motor. The pump receives a power supply from the fuel pump relay, simultaneously with the primary pump. Both pumps are operated together under all conditions.

The pump recirculates warm fuel returning from the injection pump through the fuel filter to prevent waxing of the fuel in cold conditions. This is directed into the pump feed hose from the five port valve when the fuel is below 76°C (169°F) and the bi-metallic valve is closed, by-passing the fuel cooler.

Fuel Pump Relay

The primary and secondary low pressure pumps are controlled by the ECM via a relay which is located on a bracket on the 'A' post, adjacent to the passenger compartment fusebox.

The relay coil receives a permanent battery supply via the fuel shut-off switch. The coil is energised when required by the ECM which provides an earth path. In the event of the fuel shut-off switch being tripped, the power supply to the relay coil is removed, de-energising the coil and removing the power supply to the primary and secondary low pressure pump.