Fuel delivery system - Td4 (3): Description and operation

The injection pump uses the fuel as a lubricant and coolant for the pump internal components. The pump has an integral control valve which ensures that fuel delivery to the internal components is maintained in the event of a drop of fuel supply pressure. If the supply pressure falls to below 0.5 bar (7.25 lbf/in²), the valve closes and diverts all fuel to the lubrication and coolant passages within the pump in preference to supplying the injectors, preventing irreparable damage to the pump.

The ECM monitors the fuel pressure by a fuel pressure sensor located in the fuel filter. This sensor detects fuel pressure emerging from the filter and can detect low fuel supply pressure to the injector pump immediately. If the pressure falls to below 0.8 bar (11.6 lbf/in²), the ECM changes the fuelling strategy to the engine. In this instance there will be a gradual drop in engine power because the ECM will limit the injector pulse times to preserve fuel pressure in the rail and allow the vehicle to be driven safely to a stop.

The injection pump delivers a high output which is not required by the engine at all times. Excess fuel is passed from the pump to the fuel tank via the pressure control valve. At fuel temperatures above 76°C (169°F), a bi-metallic valve diverts the fuel through a fuel cooler, located above the engine cooling radiator, to cool the fuel before it returns to the tank.

The engine requires a minimum output of 200 bar (2900 lbf/in²) at start up and 300 bar (4350 lbf/in

²) at idle. The pump can deliver a maximum output pressure of up to 1300 bar (18850 lbf/in²) to cover all operating conditions.

The pump has three external connections; a LP supply, a HP output and a HP return. The connections have tapered seats which accept the coned seats of the connecting pipes which are secured with ferrule nuts. The fuel flowing through the pump is also used to cool and lubricate the pump internal components.

Pressure Control Valve

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2

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8

M19 3265

1 HP fuel input 2 Support ring 3 Body 4 Coil

4 5

6

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5 Armature 6 Spring 7 Electrical connector 8 O-ring seals

The pressure control valve is located on the pump and directly controls the pressure of fuel delivered to the fuel rail via an integral solenoid valve. The valve is sealed in the pump housing with two O-ring seals. The inner seal, which is exposed to HP fuel, has a support ring to aid sealing against the high fuel pressure.

When the ball valve is in its closed position, the coil is energised, forcing the armature to hold the ball valve on its seat against the HP output from the pump, assisted by the coil spring.

When the ball valve is in its open position, the coil is de-energised. This allows the ball valve to push the armature, against the coil spring pressure and allow the valve to open. This allows the HP pump output to pass through the open ball valve into the fuel return pipe.