and are drawn into the fuel pump. They can be seen through a transparent hose. This form of separation is entirely normal.
The visual inspection for air bubbles in the transparent hose is therefore not counted as a fault diagnosis.
Effects of faults
Poor starting when the engine is warm or cold.
Irregular idling.
Engine will not start.
Engine starts, but cuts out again immediately afterwards.
Engine has insufficient power.
Overview of the high-pressure system
Illustration shows the high-pressure system of the 2.0L Duratorq-TDCi (DW) diesel engine
E43283
1
2
3 5 4
6
Fuel injector 1
Fuel metering valve 2
Fuel pressure control valve 3
Fuel pump 4
Fuel rail 5
Fuel pressure sensor 6
Siemens common rail system Lesson 2 – Fuel System
Fuel pump
Overview
Illustration shows the fuel pump with halfshaft for timing belt drive (1.4L Duratorq-TDCi (DV) diesel engine)
E53590
1
5 6
2 3
A
B C
4
Fuel return A
High-pressure connection B
Fuel line C
Fuel metering valve (partial view) 1
High-pressure pump element (displacement unit) 2
Fuel pressure control valve 3
Eccentric 4
Halfshaft 5
Transfer pump 6
NOTE: The fuel metering valve as well as the fuel pressure control valve are part of the fuel pump and therefore must not be renewed separately during servicing.
Note: Depending on the engine version, the fuel pump is driven via the timing belt for camshaft drive (1.4L Duratorq-TDCi (DV) diesel engine) or via the exhaust camshaft (2.0L Duratorq-TDCi (DW) diesel engine).
The design and function of the fuel pump are essentially similar.
Lesson 2 – Fuel System Siemens common rail system
High-pressure generation and fuel routing in the fuel pump
E53591
1
10
13
14
11
9
10
10 11
11 12
13 13 4
B
D
8 A
C 3
2
5
7 6
Fuel line A
Fuel line (fuel quantity fed to the fuel pump) B
High-pressure connection to the fuel rail C
Fuel return D
Admission-pressure control valve 1
Strainer filter 2
Intake side of the transfer pump 3
Transfer pump 4
Fuel metering valve 5
Fuel pressure control valve 6
Filter 7
Fuel pump 8
Eccentric on the halfshaft 9
Pump element intake valve 10
Siemens common rail system Lesson 2 – Fuel System
Pump element outlet valve 11
High-pressure ring line 12
High-pressure pump elements 13
Lubrication valve 14
The fuel is drawn from the fuel tank via the fuel filter by means of the transfer pump integrated in the fuel pump.
The transfer pump delivers the fuel on to the fuel metering valve and to the lubrication valve. When the fuel metering valve is closed, the admission pressure control valve opens and routes the excess fuel back to the intake side of the transfer pump.
The lubrication valve is calibrated to always ensure sufficient lubrication and cooling in the interior of the pump.
The fuel quantity fed to the high-pressure chambers (pump elements) is determined via the
electromagnetically-operated fuel metering valve (actuated by the PCM).
The high-pressure chambers are formed by three pump elements (displacement units), each offset by 120 degrees.
The fuel pressure control valve is located in the high-pressure channel, between the high-pressure chambers and the high-pressure outlet port to the fuel rail. This electromagnetically-operated valve which is actuated by the PCM controls the fuel pressure which is fed into the fuel rail via the high-pressure outlet port.
The fuel pressure control valve routes the excess fuel into the fuel return line and back to the fuel tank.
Principle of high-pressure generation (intake stroke)
E53592
1 1
5
4 3
2
A B
C
2 3
4 5 D
Fuel intake A
Fuel delivery B
Fuel feed from the fuel metering valve C
Fuel outlet port to the high-pressure ring line D
Intake valve 1
Exhaust valve 2
Piston 3
Halfshaft 4
Eccentric 5
The three pump plungers are actuated by the rotary movement of the fuel pump halfshaft and the eccentric
When the fuel metering valve opens the feed to the high-pressure chambers, the fuel pressure from the
Lesson 2 – Fuel System Siemens common rail system
high-pressure chambers. If the transfer pressure exceeds the internal pressure of the high-pressure chamber (pump plunger in TDC position), the intake valve opens.
Fuel is now forced into the high-pressure chamber, which moves the pump plunger downwards (intake stroke).
Principle of high-pressure generation (delivery stroke)
When the pump plunger passes BDC, the intake valve closes due to the increasing pressure in the high-pressure chamber. The fuel in the high-pressure chamber can no longer escape.
As soon as the pressure in the high-pressure chamber exceeds the pressure in the high-pressure channel, the exhaust valve opens and the fuel is forced into the high-pressure channel (delivery stroke).
The pump plunger delivers fuel until TDC is reached.
The pressure then drops and the exhaust valve closes.
The pressure on the remaining fuel is reduced. The pump plunger moves downwards.
If the pressure in the high-pressure chamber falls below the transfer pressure, the intake valve reopens and the process starts again.
Service instructions Specific versions only:
After installing a new fuel pump, the adapted values of the fuel metering valve must be reset with the help of the IDS.
Fuel rail and high-pressure fuel lines
Fuel rail
Illustration shows the system in the 2.0L Duratorq-TDCi (DW) diesel engine
E53593
2
3 4
1
High pressure fuel lines (to the fuel injectors) 1
High-pressure fuel line (to the fuel pump) 2
Fuel rail 3
Fuel pressure sensor 4
The fuel rail is made of forged steel.
The fuel rail performs the following functions:
• stores fuel under high pressure and
• minimises pressure fluctuations.
Pressure fluctuations are induced in the high-pressure fuel system due to the operating movements in the high-pressure chambers of the fuel pump and the opening and closing of the fuel injectors.
The fuel rail is therefore designed in such a way that its volume is sufficient, on the one hand, to minimise pressure fluctuations. On the other hand, the volume in the fuel rail is sufficiently low to build up the fuel pressure required for a quick start in the shortest possible time.
The fuel supplied by the fuel pump flows via a high-pressure line to the fuel rail (high-pressure accumulator). The fuel is then sent to the individual fuel injectors via the four fuel injection lines which are all the same length.
Siemens common rail system Lesson 2 – Fuel System
When fuel is taken from the fuel rail for an injection process, the pressure in the fuel rail remains almost constant.
Fuel pressure sensor
NOTE: The fuel pressure sensor must not be removed from the fuel rail during servicing. If the fuel pressure sensor is faulty, the fuel rail must be renewed along with the fuel pressure sensor.
There is a fuel pressure sensor located on the fuel rail so that the engine management system can precisely determine the injected fuel quantity as a function of the current fuel pressure in the fuel rail (see also "Lesson 4 - Sensors").
High-pressure fuel lines
NOTE: The bending radii are exactly matched to the system and must not be changed.
NOTE: After disconnecting one or more high-pressure fuel lines, these must always be renewed. The reason for this is that leaks can occur when retightening due to distortion of the connections of the old lines.
The high-pressure fuel lines connect the fuel pump to the fuel rail and the fuel rail to the individual fuel injectors.
Fuel injectors
E53594
1
7
6
8
9 10
4 11
6
7 2 3
1
E D
C 2
3
4 5 6
A B
E D C
Fuel injector (1.4L Duratorq-TDCi (DV) diesel engine and 1.8L Duratorq-TDCi (Kent) diesel engine)
A
Fuel injector (2.0L Duratorq-TDCi (DW) diesel engine)
B
Fuel injector head C
Hydraulic servo system D
Fuel injector nozzle E
Connector for PCM 1
Piezo actuator 2
High-pressure fuel line connection 3
Combustion chamber seal 4
Lesson 2 – Fuel System Siemens common rail system
Emission standard coding 5
Fuel return connection 6
Retainer 7
Fuel return adapter 8
O-ring 9
Adapter fastening clip 10
Plastic bush 11
Depending on the engine version, fuel injectors of different designs are used. Their basic construction and function are, however, largely the same.
The start of injection and the injected fuel quantity specified by the PCM are implemented by means of the piezo-electrically-controlled fuel injectors.
Depending on engine speed and engine load, the fuel injectors are actuated by the PCM with an opening voltage of approximately 70 V. The piezo effect causes the voltage within the piezo element to rise to
approximately 140 V.
The fuel injectors inject the appropriate fuel quantity per working cycle for all engine operating conditions into the combustion chambers.
Extremely short switching times of approximately 200 às permit extremely rapid reaction to changes in the operating conditions. The fuel quantity to be injected can thus be metered very precisely.
The fuel injectors are divided into three assemblies:
• fuel injector head, including the piezo actuator,
• hydraulic servo system,
• fuel injector nozzle.
NOTE: The fuel injectors cannot be dismantled during repair as this results in their destruction.
NOTE: The wiring harness connectors of the fuel injectors must on no account be unplugged when the engine is running. The piezo actuators remain expanded for a certain period after the power is cut off in the charging phase, i.e. the nozzles remain open. Effect:
continuous injection and engine damage.
The combustion chamber seals must be renewed during servicing.
Special features
1.4L Duratorq-TDCi (DV) diesel engine:
• In newer versions, a distinction is made between Emission Standard III and Emission Standard IV fuel injectors. A code is stamped onto the fuel injector shaft for this purpose:
– E3 = Emission Standard III, – E4 = Emission Standard IV.
2.0L Duratorq-TDCi (DW) diesel engine:
• A guide bushing located in the lower part of the cylinder head and a plastic bushing on the fuel injector shaft serve to fasten the fuel injector.
Siemens common rail system Lesson 2 – Fuel System
How fuel injectors work
Fuel injector closed
E53595
4
3
2
1
8 2 6
3 3
5
7
High-pressure feed 1
Control piston 2
Fuel return 3
Piezo actuator 4
Mushroom valve 5
Control chamber 6
Nozzle prechamber 7
Nozzle needle 8
The fuel is fed at high pressure from the fuel rail via the high-pressure feed into the control chamber and the nozzle prechamber.
The piezo actuator is de-energised and the orifice to the fuel return is closed by means of the spring-loaded mushroom valve.
The hydraulic force now exerted on the nozzle needle by the high fuel pressure in the control chamber via the control piston is greater than the hydraulic force acting on the nozzle needle, as the surface of the control piston in the control chamber is greater than the surface of the nozzle needle in the nozzle prechamber.
The nozzle needle of the fuel injector is closed (no injection).
Lesson 2 – Fuel System Siemens common rail system
Fuel injector opens
E53596
3
6
2
8
1 4
3
2
7
9 5
9
High-pressure feed 1
Control piston 2
Fuel return 3
Piezo actuator 4
Mushroom valve 5
Control chamber 6
Nozzle prechamber 7
Nozzle needle 8
Valve piston 9
The piezo actuator which is energised by the PCM expands (charging phase) and pushes against the valve piston.
The mushroom valve opens the orifice which connects the control chamber with the fuel return.
This results in a pressure drop in the control chamber and the hydraulic force acting on the nozzle needle is now greater than the force acting on the control piston in the control chamber.
This causes the nozzle needle to be moved upwards, the fuel injector opens and the fuel enters the combustion chamber via the spray holes.
The piezo actuator is deactivated at a certain point determined by the PCM. The valve piston moves back upwards and the mushroom valve closes off the control chamber.
As soon as the pressure in the control chamber exceeds the pressure in the nozzle prechamber, the nozzle needle closes off the spray holes and injection ends.
Siemens common rail system Lesson 2 – Fuel System
Fuel injector identification markings
E53597
f e
d c b
a
Identification number coding:
a. Classification (2.0L Duratorq-TDCi (DW) diesel engine only)
b. Ford part number
c. Year of manufacture (C = 2003, D = 2004 . . . ) d. Month (A = January, B = February, . . . L =
December) e. Day (01 ... 31)
f. Part number (00001 ... 99999)
The identification markings of the piezo fuel injectors are located on the fuel injector head.
Classification (correction factor):
• The fuel injectors of the 2.0L Duratorq-TDCi (DW) diesel engine are marked with a number for classification purposes.
• A total of three classifications are available:
– 4, 5 and 6
• When installing one new fuel injector, it should be noted which classification is marked on the fuel injector.
• All the fuel injectors installed in an engine must have the same classification.
When installing all new fuel injectors, the new fuel injectors may have a different classification, For example, if the old fuel injectors are in class "5" and the new ones are all class "4", this is permissible.
The change of classification must nevertheless be communicated to the PCM with the help of the IDS.
Effects of faulty fuel injector(s) (mechanical faults)
Increased black smoke production.
Fuel injector leaks.
Increased combustion noise as a result of coked nozzle needles.
Irregular idling.
Lesson 2 – Fuel System Siemens common rail system
Fuel filter
How fuel preheating works
E69908
2 3
4
5 6 8
7 1
Fuel return (to the fuel filter) 1
Fuel return (to the fuel tank) 2
Fuel line (to the fuel pump) 3
Fuel filter minder gauge 4
Water-in-fuel sensor (certain markets only) 5
Water drain screw 6
Water-in-fuel sensor wiring harness 7
Fuel line (from the fuel tank) 8
Fuel preheating works via a bimetallically-controlled control valve. Fuel flow control only works at fuel temperatures between 15 and 45 ° C.
Fuel temperature below 15 °C:
• The bimetallically-controlled control valve is fully open; a defined fuel return volume from the fuel pump is returned directly to the fuel filter via the control valve.
Fuel temperature greater than 45 °C:
• The bimetallically-controlled control valve is fully closed; the full fuel return volume flows past the fuel filter into the fuel tank.
Fuel filter with water-in-fuel sensor (certain markets only)
After installing a new fuel filter, a parameter reset of the values for the water-in-fuel sensor must be carried out with the help of the IDS.
Denso common rail system Lesson 2 – Fuel System
Overview of the high-pressure system
Illustration shows the system in the 2.4L Duratorq-TDCi
E69809
High-pressure line 1
Leak-off pipe 2
Fuel injection line 3
Fuel injector 4
Pressure relief valve 5
Fuel rail (common rail) 6
Fuel metering valve 7
Fuel pressure sensor 8
Fuel temperature sensor 9
Fuel pump 10
Fuel return 11