Fuel Pressure Regulator and Residual Pressure, Checking

Fuel Pressure, Checking

Special tools, testers and auxiliary items required

^ High pressure fuel gauge

CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. The fuel system is under pressure! Before opening the system, place rags around the connection area. Then release the pressure by carefully loosening the connection.






- Remove the fuel supply line - 3 - and catch leaking fuel using a rag.






- Install a High pressure fuel gauge in place of the fuel supply line.

- Open the shut-off valve of the High pressure fuel gauge.

- Switch the ignition on and off until the fuel pressure on no longer rises.

- Check the indicated fuel pressure on the High pressure fuel gauge.

Specified value: 3.5 to 5.0 bar.

If the fuel pressure is OK, check the residual pressure.

- If specified value is obtained:

- Check the return line between the fuel filter and the fuel pump for kinks and blockage.

If no malfunction is found in the return line between the fuel filter and the fuel pump:

- The pressure relief valve in the fuel filter is malfunctioning, replace the fuel filter.

If specified value is not obtained:

- Check the fuel pressure in front of the fuel filter.






- Connect a High pressure fuel gauge between the fuel filter and the fuel supply line.

- Open the shut-off valve of the High pressure fuel gauge.

- Start the engine and let it run at idle.

CAUTION!
Shut-off valve must only be closed slowly. At a fuel pressure of 8 bar, shut-off valve must be opened again immediately to prevent damage to pressure measuring device.






- Slowly close the shut-off valve of the High pressure fuel gauge. Pressure must increase to min. 6.0 bar. If 6 bar is reached, open shut-off valve again immediately!

If the fuel pressure increases:

- The pressure relief valve in the fuel filter malfunctioning, replace the fuel filter.

If the fuel pressure does not increase:

- Replace the fuel pump.

Final Procedures

After the repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory.
2. If necessary, erase the DTC memory.
3. If the DTC memory was erased, generate readiness code.

End of diagnosis.