Fuel System Overview
Fuel System Overview
• Follow the guidelines for a clean working environment when working on the fuel system. Refer to => [ Clean Working Conditions ] Clean Working Conditions.
• Always follow these rules before and during work.
Follow the points below to avoid running the high pressure fuel pump dry (very low tolerances) and to start the engine quickly after replacing the components:
• If the fuel system components between the fuel tank and high pressure fuel pump were removed or replaced, the fuel system must be bled. Refer to => [ Fuel System, Bleeding ] Fuel System, Bleeding.
• It is necessary to bleed the fuel system before starting the engine for the first time if the fuel pump, the fuel line (between the fuel tank and the fuel high pressure pump) or the fuel filter were removed.
• If the fuel high pressure pump was removed or replaced, then bleed the fuel system before starting the engine for the first time.
Fill the fuel tank after installing the high pressure pump. Refer to => [ Fuel Tank, Filling with Fuel after Installing High Pressure Pump ] General Information.
1 - Fuel Return Line
• To fuel tank
• The fuel return line must not be bent, damaged or plugged
2 - Fuel Supply Line
• Coming from the fuel filter
3 - Fuel Return Line Banjo Fitting
• 25 Nm
4 - Fuel Temperature Sensor (G81)
5 - Bolt
6 - Bracket
7 - Fuel Pressure Regulator Valve (N276)
• Installed on cylinder bank 1
• Cannot be used again
• The adaptation values must be adapted after replacing the high pressure pump or the fuel pressure regulator valve, refer to "Guided Functions" in the vehicle diagnostic tester.
• Removing and installing, refer to => [ Fuel Pressure Regulator Valve (N276) ] Service and Repair
8 - Bolt
9 - Bracket
10 - High Pressure Fuel Line
• Between the high pressure pump and fuel rail
11 - High Pressure Fuel Line
• Between the cylinder bank 1 fuel rail and cylinder bank 2 fuel rail
• Before reusing the "fuel high pressure line", check the sealing cones for damage such as scratches or corrosion. Replace if damaged.
• If the high pressure line is not OK, always replace the high pressure line
12 - Fuel High Pressure Pump
• With fuel metering valve (N290)
• Fill the fuel tank after replacing the fuel high pressure pump (never run dry). Refer to => [ Fuel Tank, Filling with Fuel after Installing High Pressure Pump ] General Information.
• The adaptation values must be adapted after replacing the high pressure pump or the fuel pressure regulator valve (N276). Refer to "Guided Functions" in the vehicle diagnostic tester.
• High pressure pump assembly overview, refer to => [ High Pressure Pump Overview ] Service and Repair.
• Removing and installing, refer to => [ High Pressure Pump ] High Pressure Pump.
13 - Fuel Return Lines
• Do not disassemble the fuel return lines. Replace them completely with the pressure retention valve.
• Bleed the fuel system after replacing, refer to => [ Fuel Tank, Filling with Fuel after Installing High Pressure Pump ] General Information.
14 - Bolt
• 5.5 Nm
• Injector unit cover to cylinder head cover
15 - Injection Unit Cover
16 - Tensioning Bracket
• Injectors and tensioning brackets that have been removed and are being reinstalled may only be installed in the same cylinder.
• If the injector unit (injector) is being replaced, then the tension bracket must also be replaced.
17 - Hex Shoulder Nut
• 10 Nm
• For the tension bracket
18 - Bolt
• 22 Nm
• For the cylinder bank 2 fuel rail
19 - Fuel Pressure (FP) Sensor (G247)
• 30 Nm
• Installed on cylinder bank 2
• Removing and installing, refer to => [ Fuel Pressure Sensor (G247) ] Service and Repair
20 - Seal
• Replace
21 - Fuel High Pressure Lines
• 25 Nm
• For cylinder bank 2
22 - Fuel rail
• For cylinder bank 2
23 - Seals
• Replace
24 - Hex Shoulder Nut
• 10 Nm
• For the tension bracket
25 - Injector
• Mark the part allocations for reinstallation and follow them when installing
• Removing and installing, refer to => [ Fuel Injectors ] Fuel Injectors
26 - Bolt
• 5.5 Nm
• Injector unit cover to cylinder head cover
27 - Injection Unit Cover
28 - Seal
• Replace
29 - Fuel High Pressure Lines
• For cylinder bank 1
30 - Bolt
• 22 Nm
• For the cylinder bank 1 fuel rail
31 - Fuel Return Lines
• Do not disassemble the fuel return lines. Replace them completely with the pressure retention valve.
• Bleed the fuel system after replacing, refer to => [ Fuel Tank, Filling with Fuel after Installing High Pressure Pump ] General Information.
32 - Pressure Retaining Valve or Restrictor
• The type of component that was installed is dependent upon the model year
• The check valve always maintains a residual pressure (control quantity) of approximately 10 bar (145 psi) in the fuel return lines.
• The restrictor always maintains a residual pressure (control quantity) of approximately 4 bar (58 psi) in the fuel return lines.
• The Piezo injectors need this control quantity for their function.
• The check valve or the restrictor can be replaced only with the complete fuel return lines.
• Bleed the fuel system after replacing. Refer to => [ Fuel Tank, Filling with Fuel after Installing High Pressure Pump ] General Information
• Check pressure retaining valve. Refer to => [ Fuel Return Check Valve, Checking ] Fuel Return Check Valve, Checking
• Check the restrictor, refer to => [ Restrictor in the Fuel Return Line, Checking ] Restrictor In the Fuel Return Line, Checking