Service instructions
After all work on the high-pressure system, a fuel system leak test must be performed with the help of the IDS.
Fuel pump
Illustration shows the fuel pump of the 2.4L Duratorq-TDCi
E69909
6 7 8
9
C 10
11 12
13
B
A
1
14
2 3
4
5
High-pressure fuel to the fuel rail A
Fuel return B
Fuel line C
High-pressure chamber exhaust valve 1
High-pressure chamber intake valve 2
Pump plunger 3
Fuel metering valve return spring 4
Fuel metering valve 5
Admission pressure control valve (pump interior pressure)
6
Transfer pump (rotor pump) 7
Fuel intake 8
Fuel filter 9
Eccentric cam ring 10
Eccentric cam 11
Halfshaft 12
Fuel tank 13
Overflow throttle valve 14
Denso common rail system Lesson 2 – Fuel System
Design
The fuel pump provides the interface between the low-pressure and high-pressure systems. Its function is to always provide sufficient compressed fuel under all operating conditions and for the entire service life of the vehicle.
Low-pressure part:
• The transfer pump draws fuel out of the fuel tank via the fuel intake.
• The pump internal pressure is adjusted via the admission pressure control valve. This ensures that sufficient lubrication and cooling are always provided for the fuel pump components. Excess fuel is transferred to the intake side of the transfer pump via the admission pressure control valve.
• A portion of the fuel is transferred to the fuel metering valve from the transfer pump. The fuel quantity delivered to the high pressure chambers is determined by the opening cross-section of the fuel metering valve.
• The small restriction bore in the overflow throttle valve provides for automatic ventilation of the fuel pump. The entire low-pressure system is designed to allow a defined quantity of fuel to flow back into the fuel tank via the overflow throttle valve. This assists cooling of the fuel pump.
High-pressure part:
• A total of two high-pressure chambers, each with one pump plunger, are used for high-pressure generation.
• The pump plungers are driven via an eccentric cam, which is in turn driven by the halfshaft (principle similar to the Bosch common rail system).
• The fuel pump permanently generates the high system pressure for the fuel rail.
Lesson 2 – Fuel System Denso common rail system
Principle of high-pressure generation
E69910
1 2
3
4 C A
6
B 5
Pump plunger 1 A
Pump plunger 2 B
To the fuel rail C
Intake valve 1
Exhaust valve 2
Eccentric cam 3
Eccentric cam ring 4
Fuel metering valve 5
Halfshaft 6
Denso common rail system Lesson 2 – Fuel System
The rotary movement of the halfshaft is converted to a reciprocating movement by the eccentric cam. The eccentric cam ring transfers the reciprocating movement to the pump plungers.
The pump plungers are arranged offset by 180 degrees.
This means that during a reciprocating movement, pump plunger 1 performs exactly the opposite movement to pump plunger 2.
The eccentric cam generates an "upward" stroke:
• Pump plunger 1 moves in the direction of TDC, thus pressurising the fuel and delivering it to the fuel rail via the exhaust valve. The intake valve is pressed into its seat by the delivery pressure.
• Pump plunger 2 is moved by the tension spring force in the direction of BDC. Due to the high pressure in the fuel rail, the exhaust valve is pressed into its seat.
The pump internal pressure opens the intake valve and fuel flows into the high-pressure chamber.
The eccentric cam generates a "downward" stroke:
• The process is the reverse to that previously described.
Programming the fuel pump (fuel metering valve)
After installing a new fuel pump/fuel metering valve and/or PCM, the fuel metering valve of the fuel pump must be programmed with the help of the IDS.
Service instructions
After installing a new fuel pump or fuel metering valve, the fuel pump must be adapted with the help of the IDS.
Fuel rail and high-pressure fuel lines
Fuel rail
1
2 3
4 5
1
2 3
4 5
E98851
High-pressure fuel lines (to the fuel injectors) 1
Pressure relief valve 2
Fuel rail 3
Fuel pressure sensor 4
High-pressure fuel lines (to the fuel pump) 5
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 solenoid valves on the fuel injectors.
Consequently, the fuel rail is designed in such a way that, on the one hand, it possesses sufficient volume to minimise pressure fluctuations, but, 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 passes through a high-pressure line to the 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.
When fuel is taken from the fuel rail for an injection process, the pressure in the fuel rail remains almost constant.
Lesson 2 – Fuel System Denso common rail system
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 pressure sensor
The fuel pressure sensor must not be renewed separately in the event of a fault. The whole fuel rail must always be renewed in the event of a fault.
Pressure relief valve
The pressure relief valve opens at a fuel pressure of above 2,200 bar. It serves as a safeguard in the event of a malfunction in the high-pressure system. This prevents damage caused by excessive fuel pressure in the high-pressure system.
The pressure relief valve works as a disposable valve.
This means that it must be renewed after it has been triggered once, as it will no longer seal properly.
NOTE: The pressure relief valve cannot be renewed separately during servicing. The entire fuel rail must be renewed in the event of a fault.
NOTE: Triggering of the pressure relief valve is frequently caused by a defective fuel metering valve.
Any triggering of the pressure relief valve is detected by the PCM, which then sets an appropriate DTC (Diagnostic Trouble Code) and actuates the MIL (Malfunction Indicator Lamp).
Denso common rail system Lesson 2 – Fuel System
Fuel injectors
Design
E98372
6 7
5 4 3
8 9
1
10
2
11
Solenoid valve 1
Fuel rail pressure 2
Fuel strainer 3
Piston rod 4
Nozzle needle spring 5
Nozzle needle 6
Combustion chamber seal 7
Fuel rail pressure 8
Valve seat 9
Leak-off 10
Control chamber 11
NOTE: The combustion chamber seals must not be reused.
The exact procedure for the correct installation of the fuel injectors can be found in the current Service Literature.
Start of injection and injected fuel quantity are adjusted via the fuel injectors.
Lesson 2 – Fuel System Denso common rail system
In order to achieve the optimal injection timing and precise injected fuel quantity, special fuel injectors with a hydraulic servo system and electrical actuator unit (solenoid valve) are used.
The fuel injectors are actuated directly by the PCM.
The PCM specifies the injected fuel quantity and the injection timing.
The fuel injectors are divided into different function blocks:
• injector nozzle,
• hydraulic servo system,
• solenoid valve.
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.
Service instructions
Illustration shows top view of fuel injector
E69913
1
3
2
Solenoid valve connector 1
16-digit correction factor 2
Leak-off pipe connection 3
After installing one or more new fuel injectors, the following service functions must be performed with the help of the IDS:
• entry of the correction factors of the fuel injectors and
• adaptation of pilot injection by the fuel injectors.
Entry of the correction factors:
Inside the hydraulic servo system there are various restrictors with extremely small diameters which have specific manufacturing tolerances.
These manufacturing tolerances are given as part of a correction factor, which is located on the housing of the fuel injector.
To ensure optimum fuel metering, the PCM must be informed when a fuel injector is changed.
Furthermore, after new PCM software has been loaded via IDS, the fuel injectors must also be configured with this software.
This is achieved by entering the 16-digit correction factor into the PCM with the help of the IDS, taking into account the relevant cylinder.
Note: If the correction factors are not entered properly, the following faults can occur:
• increased black smoke formation,
• irregular idling,
• increased combustion noise,
• engine will not start.
Adaptation of pilot injection by the fuel injectors:
• The pilot injection of each fuel injector must be optimally preset so that the engine runs with as little combustion noise as possible.
• The cylinder acceleration of each cylinder is recorded and if necessary the pilot injection adapted using the
"Adaptation of pilot injection by the fuel injectors"
service function.
• If adaptation of pilot injection by the fuel injectors is not correctly completed, the combustion noise will be louder.
Denso common rail system Lesson 2 – Fuel System
Tick the correct answer or fill in the gaps.
1. Which of the following statements about the low-pressure system is incorrect?
a. Fuel lines may be blocked due to foreign bodies or bending.
b. The in-tank fuel pump supplies fuel to the high-pressure pump.
c. The fuel filter must be dewatered regularly within the specified maintenance intervals.
d. Faulty valves or pipes in the tank venting system can impair the flow of fuel through the low-pressure system.
2. Which of the effects listed does not apply to a blocked fuel filter?
a. Engine demonstrates increased knocking noise at partial load.
b. Engine has insufficient power.
c. Poor engine starting performance when both cold and hot.
d. Engine will not start.
3. What is the function of the transfer pump?
a. The transfer pump controls fuel supply to the high-pressure chambers.
b. The transfer pump delivers the required fuel to the fuel pump.
c. The transfer pump generates the high pressure required for injection.
d. The transfer pump cuts in as required when the high pressure in the fuel rail falls below a minimum.
4. Which of the following statements about the high-pressure system is true?
a. Bosch common rail systems have only solenoid valve-controlled fuel injectors.
b. The fuel rail is designed in such a way that pressure fluctuations are maximised.
c. After disconnecting a high-pressure fuel line, a new one must always be installed.
d. The fuel metering valve is part of the fuel rail and must not be renewed separately during servicing.