Fuel Delivery and Air Induction: Description and Operation
Incorrect Fueling
Special tools, testers and auxiliary items required
• Trim Removal Wedge (3409)
• Hose (VAS 6551/5-2)
• Suction Pump (VAS 5226)
Fueling incorrectly can cause insufficient lubrication which can lead to irreversible damage to the high pressure components, especially the high pressure pump. Damage in the form of seizing and particle abrasion can be expected. These particles will cause further damage in the pressure control valve and the injectors.
• This information guides the reader through the individual procedures like a flowchart.
Was the engine started with the incorrect fuel?
Yes, refer to => [ Step 1 (Engine Was Started with Incorrect Fuel) ].
No, refer to => [ Step 2 (Engine Was Not Started with Incorrect Fuel) ].
Step 1 (Engine Was Started with Incorrect Fuel)
- Drain the fuel tank as much as possible through the filler neck using the fuel extracting device (VAS 5190). Refer to => [ When the Tank is More Than 3/4 Full ] Procedures.
- Remove the rear seat bench.
- Remove the flange cover - 1 - using the trim removal wedge (3409) - arrows -.
- Disconnect the fuel return line (blue or with a blue mark) - 1 -. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Coupling, Disconnecting.
The fuel supply line is under pressure. Wear protective goggles and protective clothing in order to avoid injury and contact with the skin. Wrap a cloth around the connection before removing a fuel hose. Remove the hose connection carefully to release the pressure.
If the battery is connected, make sure that the fuel pump is not activated when the drivers door is opened. Fuel may leak out when the system is open.
- Connect the hose (VAS 6551/5-2) from the pressure tester to the fuel return line - 1 -.
- Place the free end of the hose (VAS 6551/5-2) into a container.
- Connect the vehicle diagnostic tester and perform the Guided Function "Activate Fuel Pump".
• The fuel pump is activated.
- Repeat this procedure as necessary until the fuel tank is completely empty.
- Remove the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.
- Check the fuel tank for particles.
- Empty the fuel delivery unit reservoir.
- Check the reservoir visually for large contaminants and particles and on the screen.
Are there any particles?
Yes, refer to => [ Step 3 (Particles in the Fuel Delivery Unit and Reservoir) ].
No, refer to => [ Step 4 (No Particles in the Fuel Delivery Unit and Reservoir) ].
Step 2 (Engine Was Not Started with Incorrect Fuel)
- Drain the fuel tank as much as possible through the filler neck using the fuel extracting device (VAS 5190). Refer to => [ When the Tank is More Than 3/4 Full ] Procedures.
- Remove the rear seat bench.
- Remove the flange cover - 1 - using the trim removal wedge (3409) - arrows -.
- Disconnect the fuel return line (blue or with a blue mark) - 1 -. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Coupling, Disconnecting.
The fuel supply line is under pressure. Wear protective goggles and protective clothing in order to avoid injury and contact with the skin. Wrap a cloth around the connection before removing a fuel hose. Remove the hose connection carefully to release the pressure.
If the battery is connected, make sure that the fuel pump is not activated when the drivers door is opened. Fuel may leak out when the system is open.
- Connect the hose (VAS 6551/5-2) from the pressure tester to the fuel return line - 1 -.
- Place the free end of the hose (VAS 6551/5-2) into a container.
- Connect the vehicle diagnostic tester and perform the Guided Function "Activate Fuel Pump".
• The fuel pump is activated.
- Repeat this procedure as necessary until the fuel tank is completely empty.
- Fill the fuel tank with 5 liters of diesel fuel.
- Drain the fuel tank completely as described above.
- Reconnect the fuel return line.
- Replace the fuel filter. Refer to Maintenance Procedures Rep.
- Fuel the vehicle and perform a road test.
End
Step 3 (Particles in the Fuel Delivery Unit and Reservoir)
- Clean the fuel delivery unit and fuel tank using the suction pump (VAS 5226).
- Install the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.
- Fill the fuel tank with 5 liters of diesel fuel.
- Drain the fuel tank completely as described in step 2.
- Replace the following high pressure components:
• High pressure pump.
• High pressure line.
• Fuel rail (high pressure reservoir) including the fuel pressure regulator valve (N 276) and fuel pressure sensor (G 247).
• Fuel Injector.
• Fuel return lines (overflow lines).
• Fuel filter, refer to Maintenance Procedures
- Fuel the vehicle.
- Bleed the fuel system.
- Perform a road test.
End
Step 4 (No Particles in the Fuel Delivery Unit and Reservoir)
- Fill the fuel tank with 5 liters of diesel fuel.
- Drain the fuel tank completely as described in step 2.
- Replace the high pressure pump.
Only perform the steps below if the high pressure pump is faulty and has been removed.
- Remove the bolts - arrows - and the metering unit - A - from the OLD high pressure pump.
- Check the metering unit and high pressure pump for particles.
Are there any particles?
Yes, refer to => [ Step 5 (Particles in the High Pressure Pump) ].
No, refer to => [ Step 6 (No Particles in the High Pressure Pump) ].
Step 5 (Particles in the High Pressure Pump)
- Replace the following high pressure components:
• High pressure line.
• Fuel rail (high pressure reservoir) including the fuel pressure regulator valve (N 276) and fuel pressure sensor (G 247).
• Fuel injector.
• Fuel return lines (overflow lines)
• Fuel filter, refer to Maintenance Procedures.
- Fuel the vehicle.
- Bleed the fuel system.
- Perform a road test.
End
Step 6 (No Particles in the High Pressure Pump)
- Replace the fuel filter. Refer to Maintenance Procedures.
- Bleed the fuel system.
- Fuel the vehicle and perform a road test.
End