Residual Pressure, Checking

Fuel Pump, Checking

Special tools, testers and auxiliary items required

• Pressure Tester (VAS 6550)

• Remote Control (V.A.G 1348/3A)

• Test Instrument Adapter/DSO (5-pin) (VAS 5565)

• Multi-meter (V.A.G 1715)

• Wrench (T10202)

• Torque Wrench (40-200 Nm) (V.A.G 1332)

• Measuring Container, 2 Liter

Residual Pressure, Checking

• Fuel pressure is OK and the (VAS 6550) is connected. Checking the fuel pressure, refer to => [ Fuel Pressure, Checking ]. Fuel Pressure, Checking





Sequence

- Activate the fuel pump with output Diagnostic Test Mode (DTM) to build fuel pressure.

- Check the fuel pressure on the (VAS 6550).

• Target value: 4.0 to 7.0 bar

- Watch the pressure decrease on the (VAS 6550). After 10 minutes the pressure must not drop below a 3.0 bar decrease.

If the pressure drops further:

- Activate the fuel pump with output DTM to build fuel pressure.

- Close the shut off valve - B - on the (VAS 6550) as soon as pressure accumulates. The level is perpendicular to the direction of flow.





If Pressure No Longer Drops Now

• Check for the leak on the engine side. Repeat the residual pressure check. Close the shut off valve - A - this time to determine if there actually is a leak on the engine side.

- Check the fuel pipe to high pressure fuel pump for leaks.

If no malfunction can be found:

- Replace the high pressure fuel pump. Refer to => [ High Pressure Fuel Pump ] High Pressure Fuel Pump.

If The Pressure Drops Again

Check for the leak on the fuel tank side. Proceed as follows:

- Check the fuel line to fuel filter for leaks.

If no malfunctions are found on fuel line:

- Check the pressure retention valve in the fuel delivery unit. Proceed as follows:

- Disconnect the fuel supply line - arrow - from the fuel filter.





- Connect the (VAS 6550) between the fuel filter and fuel supply line using adapter (VAS 6550/1) and (VAS 6550/2).





- Make sure the drain is closed and the shut off valves are open.

- Activate the fuel pump with output DTM to build fuel pressure.

- Check the fuel pressure on the (VAS 6550).

• Target value: 4.0 to 7.0 bar

- Close the shut off valve - A - once pressure has increased.





- Watch the pressure decrease on the (VAS 6550). After 10 minutes the pressure must not drop below a 3.0 bar decrease.

If the pressure drops:

- If the pressure retention valve in the fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel System Components.

If the pressure does not drop:

- The pressure retention valve in the fuel pump is OK. The pressure relief valve in the fuel filter is faulty. Replace the fuel filter.