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

The four injectors are located in the cylinder head, between the four valves in each cylinder. Each injector is sealed into the cylinder head with a copper washer. Two studs in the head locate a plate on the injector which is secured with two nuts on the studs. Each stud has an external Torx fitting on the end, which allows the stud to be wound from the head and simultaneously extract the injector from its bore.

Each injector has an electrical connector for power supply and connections to the ECM. The top of each injector is fitted with a fuel return pipe which allows fuel used in the operation of the injector to return to the tank. Each injector only uses approximately 50% of the fuel delivered to it. The remaining 50% is used to cool the injector and is passed to return via the fuel return pipe. The injectors are sensitive to fuel pressure and if pressure in the fuel rail falls to below 0.6 bar (8.7 lbf/in²) the injectors will not deliver the correct fuel requirements resulting in poor emissions and driveability.

Each electronic injector has a solenoid valve which, when energised, allows a ball valve to lift off its seat. This allows pressurised fuel to lift a needle valve in the injector nozzle and spray a finely atomised jet of fuel into the cylinder. Fuel which spills past the ball valve is directed into a return line which is connected to the fuel return from the HP injector pump.

Each injector has an electrical connector which provides a 12V direct supply from the main relay and connections to the ECM. If the battery voltage falls to between 6V and 9V, the operation of the injector solenoid will be impaired affecting, acceleration, maximum speed and idle. Battery voltage below 6V will result in the injectors not operating.

Each injector solenoid is controlled separately by the ECM which provides an earth path to open the injector nozzle at the correct time and for a calculated period to provide a metered injection of fuel into the cylinder. The ECM uses signals from other sensors and a programmed fuelling strategy to ensure that the precise amount of fuel is injected at the correct timing for maximum fuel efficiency and minimum emissions.

Fuel Rail

The metal fuel rail is a forged steel tube mounted on the cylinder head and secured with two cap screws. The rail has five threaded bosses with machined taper seats. The central threaded boss is for the HP fuel feed pipe from the injector pump. The four remaining bosses are for connection to each injector. Each pipe has a cone end which seals with the tapered seat in the rail and a similar seat on the injector.

A fuel rail pressure sensor is fitted into a threaded bore in the LH end of the rail. The sensor is connected to ECM connector C0606 via the engine harness which supplies a 5V power supply, earth and signal connections. The sensor is a diaphragm type sensor with a resistive element attached to the diaphragm. The diaphragm changes shape as the fuel pressure increases or decreases, causing the element to deflect, changing the resistive characteristics of the sensor. The sensor uses the 5V supply through the resistor to produce an analogue signal to the ECM which corresponds to the fuel pressure. The ECM compares this signal to values stored in its memory to calculate the actual fuel pressure present in the rail.

Bi-metallic Valve

The bi-metallic valve is located at the front of the engine compartment at the LH end of the fuel cooler. The valve has three connections and is connected via rubber hoses to the HP injector pump return pipe and the fuel cooler feed pipe and to the tank return line at the five-port valve.

The valve contains a bi-metallic strip which moves in relation to the temperature of the fuel flowing over it. At fuel temperatures below 76°C (169°F), the valve is closed and fuel returning from the injector pump is directed into the tank return line to the five-port valve, where it is directed into the secondary LP pump feed line. At temperatures above 76°C (169°F), the bi-metallic valve closes the return line and fuel is directed through the fuel cooler.

Pressure Relief Valve

The pressure relief valve is located below the fuel filter. A tee connection in the outlet hose from the filter is connected back into a tee connection in the fuel feed hose, upstream of the secondary LP pump. The relief valve is located in this line and controls the pressure of fluid delivered to the fuel injection pump to between 2 and 2.4 bar (29 to 35 lbf/ in²). At pressures above this, the relief valve opens allowing fuel to flow back to the fuel feed hose, decaying the pressure delivered to the injection pump. The primary reason for the relief valve is to protect the injection pump from high fuel input pressure from the secondary pump if a high voltage condition occurs.

Five Port Valve

The five-port valve is located at the bottom of the LH inner wing, near the bulkhead. The valve is manufactured from moulded plastic and is secured to the inner wing with a plastic clip.