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Td5 Technical - Fuel Supply System

The complete fuel system is brand new for the Td5 engine.

Firstly, a new moulded plastic fuel tank (fitted between the chassis rails in the Defender as on the NAS V8's) is combined with a twin-stage submerged electric VDO pump, with a swirl pot to ensure contined flow on steep or rough terrain.

The low-pressure (0.75 bar) stage of the pump feeds into a replaceable-element diesel filter, fitted to the chassis rail. To provide the very clean fuel required by the unit injectors, the filter removes particles down to around 3 microns. The filter is also fitted with a water sensor to provide a warning on the instrument pack.

Unlike most other diesel engines, the Td5 has no fuel injection pump (FIP). The second stage of the fuel pump draws fuel from the filter and pressurises it to 4 bar before supplying it to the engine at a rate of 180 litres per hour. A pressure regulator fitted to the cylinder head provides removes pressure fluctuations from the high pressure fuel, returning excess diesel to the fuel cooler.

The fuel cooler, attached to the inlet manifold, is used to reduce the temperture of the diesel returning from the injectors (via the regulator) before it is fed back to the fuel tank. The cooler uses a dedicated section of the main radiator to cool engine coolant, which in turn cools the fuel in the cooler. Without the cooler, the mean fuel temperature in the system would steadily rise with the engine running. Under high pressure injection conditions, warm fuel reduces the efficiency of the injection system. While the ECM can compensate for small fuel temperature variations by adjusting the fuel map, maintaining a supply of cool fuel gives the best economy and efficiency.

Returned fuel from the cooler goes to the rear filter, where it passes through another filter. This filter allows air to pass but not fuel, de-bubbling the fuel before it returns to the high pressure line. Any air or fuel vapour removed from the fuel is vented back to the tank.

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