Fuel delivery system - Td4 (Fuel Cooler): Description and operation

The valve intersects the fuel return line from the fuel cooler. The valve also intersects the LP supply to the secondary LP pump. A connection to this line joins the fuel return line from the bi-metallic valve to the fuel cooler return line to allow returning fuel to recirculate through the secondary pump.

The valve intersects the return to tank hose from the fuel cooler and the fuel supply hose from the primary LP pump to the secondary LP pump. A fifth connection directs fuel from the injection pump, when the bi-metallic valve is closed, to pass into the valve. This warm fuel from the injection pump is mainly directed back into the feed hose to the secondary LP pump, although some fuel is allowed to flow to the tank return hose via a 2.8 mm restrictor.

Fuel Cooler

The fuel cooler is located below the bonnet locking platform. The cooler has two brackets which locate on captive studs on the locking platform and is secured with two nuts.

The cooler comprises a tube which is bent through 180° to form two parallel connected pipes. One pipe run has aluminium loops attached which are exposed to air flow from the front of the vehicle. The loops act as heat exchangers, conducting heat from the fuel as it passes through the tube. Each end of the tube is flanged. The inlet to the cooler is connected to the bi-metallic valve by a flexible hose. The outlet from the cooler is connected by a flexible hose to the five-port valve.

Fuel Filter

The fuel filter is located in a plastic housing, adjacent to the secondary LP fuel pump, in the engine compartment on the LH inner wing. The filter assembly comprises a filter canister, a filter head unit and a low pressure sensor.

The filter is accessible by removing the filter unit from the housing. The filter canister is removed from the filter head unit by unscrewing. The filter has no water trap installed. This is because the primary LP pump operates at high speed emulsifying water in the fuel and preventing accumulations in the filter. The paper filter has an increased filter area and pore size when compared to conventional filters. These characteristics help resist the potential for waxing to occur at low temperatures.

The low fuel pressure sensor is screwed into a port in the side of the filter head unit and is connected by three wires to ECM connector C0604, pins 9, 10 and 17. Pin 9 supplies a 5V supply to the sensor, pin 10 supplies an earth and pin 17 supplies a variable signal back to the ECM which corresponds to the fuel pressure.

The sensor measures the pressure on the output side of the filter and therefore can detect a blockage within the filter or failure of the LP fuel supply. The ECM will monitor the LP sensor and, in the event of very low pressure, will stop the engine to prevent damage to the HP injector pump. Refer to HP Fuel Injection Pump description in this section for further details.