1
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Bracket with sound damping material
4
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Fuel supply to high-pressure pump
5
-
Fuel return to fuel tank
6
-
Fuel supply from fuel tank
7
-
Pressure control valve in the fuel filter
The fuel filter is installed at the front right of the fuel tank.
There are a total of three connections on the fuel filter. The fuel supply connections from the fuel tank and to the high-pressure pump are located in the centre of the two end faces of the fuel filter (conventional flow through the filter).
A pressure control valve is integrated in the fuel filter which limits the system pressure in the low pressure circuit to 4.5 bar.
Any excess quantity of fuel which is pumped through is directed back to the fuel tank via the connection located on the side of the fuel filter.
Extremely fine filtration is required for the direct petrol injection on the 1.8L Duratec-SCi engine. Up to 85% of particles larger than 5 µm need to be filtered out (in comparison: the mean pore width of a filter element for multi-point injection is approximately 10 µm).
In order to minimise the noise transferred from the pressure control valve in the fuel filter onto the vehicle, the fuel filter is embedded in a bracket which is covered with sound damping material.
When replacing the fuel filter, care must therefore be taken to ensure that the sound damping material is not damaged and that the fuel filter is correctly positioned (refer to the current workshop literature).
High-pressure system
High-pressure pump
3
-
Return to the fuel tank
4
-
Return from the fuel rail
6
-
High-pressure line connection
7
-
Supply from the fuel tank
The high-pressure pump forms a single-cylinder pump which meters the fuel pressure according to requirements. This means that the high-pressure pump only delivers as much fuel as is required for injection. This means that the delivery rate of the fuel pump is adjustable.
The high-pressure pump is mechanically driven by the camshaft via a plunger.
During the downward motion of the plunger, fuel flows under a pre-pressure of approximately 4.5 bar from the fuel supply line via the inlet valve into the pump cylinder.
During the upward stroke of the plunger this volume of fluid is compressed and pumped into the fuel rail once the pressure in the fuel rail is exceeded.
The high-pressure chamber and the fuel supply are connected by means of an integrated fuel metering valve, which is actuated accordingly by the Powertrain Control Module (PCM).
If the fuel metering valve is opened by the PCM before the pumping stroke is complete, then the pressure in the high-pressure chamber collapses and the fuel flows back into the fuel supply. A non-return valve between the high-pressure chamber and the fuel rail prevents the pressure in the fuel rail from dropping as a result of opening the fuel metering valve.
In order to achieve the required delivery rate, the fuel metering valve is closed between the bottom reversing point of the pump plunger and a certain point on the pumping stroke.
Once the required pressure has been achieved in the fuel rail, the fuel metering valve opens and prevents any further pressure increase in the fuel rail.
The delivered fuel quantity depends on the engine speed and the actuation of the fuel metering valve.
Via the fuel metering valve, the high-pressure pump provides the high-pressure injectors with the required fuel pressure in the range of 50 ... 120 bar.
The high-pressure pump forms a single component with the adapter plate. They can only be replaced as a complete unit.
Fuel rail and high-pressure injectors
5
-
O-ring, intermediate sleeve
8
-
Combustion chamber oil seal
The fuel rail is used to distribute the fuel to the individual injectors.
Pulsating variations in pressure in the high-pressure part of the fuel system arise as a result of the working action of the high-pressure pump and through the opening and closing of the injectors.
The fuel rail is mounted via an intermediate sleeve and an injector sleeve directly on the injectors. As a result no additional high-pressure lines are required.
Two positioning sleeves of different design are used for guidance. These sleeves can be replaced individually in service.
Each high-pressure injector is guided on the cylinder head by means of one injector sleeve and is secured with a retainer.
An intermediate sleeve is used to secure each of the high-pressure injectors to the fuel rail.
In this layout, the high-pressure injectors represent the interface between the fuel rail and the combustion chamber.
The role of the high-pressure injectors is to meter the fuel delivery and atomise the fuel in order to achieve a defined mixture of fuel and air within a certain part of the combustion chamber.
Depending on the desired operating state, the fuel is either concentrated (stratified) in the area around the spark plug, or evenly atomised throughout the combustion chamber (homogeneous distribution).
A combustion chamber oil seal provides a seal between each high-pressure injector and the cylinder head. This oil seal is held in an annular groove on the injector.
Note: A new special tool is used to install a new combustion chamber oil seal - Installation Kit, Combustion Chamber Oil Seal 303-128. This kit comprises the following:
- Spreader/installer 310-128/2,
- Adjusting ring 310-128/1.
