Fuel Pressure, Checking Holding Pressure In Front of High Pressure Pump

Fuel Pressure, Checking Holding Pressure In Front of High Pressure Pump

Special tools, testers and auxiliary items required

• Pressure Tester (VAS 6550) with Hose (VAS 6550/1) and Hose (VAS 6550/2)

• Vehicle Diagnostic Tester

• Measuring Container, Fuel-Resistant

Procedure






- Follow all test requirements. Refer to => [ Test Conditions ] Initial Inspection and Diagnostic Overview.

There is a risk of injury because the fuel is under high pressure.

• To reduce pressure in the fuel system, lay a clean cloth around the connector and carefully loosen connector.

- Press the release ring and disconnect the fuel line - 2 -.

• Ignore - 1 -.

- Connect the (VAS 6550) and (VAS 6550/2) to the fuel supply line.






- Connect the (VAS 6550/1) and hold it inside a fuel resistant container.








Risk of fuel leak.

• Make sure that the drain - C - is closed.

• The level is perpendicular to the direction of flow.

- Open the shut-off valves - A and B -.

• The levers point in the direction of flow.

- Connect the tester.

- Turn on the ignition and select the following menu items on the vehicle diagnosis tester :

• OBD

• Engine electronics

• Basic setting

• Empty fuel tank

- Press Start: The fuel pump starts.

- If the fuel flows without bubbles, close the drain - B -, so that the fuel pressure increases.

• The level is perpendicular to the direction of flow.

- Read the fuel pressure on the (VAS 6550) :

• Specified value: 5. 0 to 8.0 bar.

- Press the Stop button.

If the specification is not attained:

- Check the fuel delivery quantity for the fuel pump. Refer to => [ Fuel Pump Delivery Rate, Checking ] Fuel Pump Delivery Rate, Checking.

Checking Holding Pressure

- Watch the pressure fall on the (VAS 6550) while checking the holding pressure and checking for leaks:

• After 10 minutes there must be a residual pressure of at least 3 bar.

If the holding pressure drops below 3 bar:

• Check the connection between the (VAS 6550) and the fuel supply line for leaks.

• Check (VAS 6550) for leaks.

• Check fuel lines and their connections for leaks.

If no faults are detected:

• Replace the locking flange with the fuel filter and fuel pressure regulator. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.

- Repeat the residual pressure check.

If there are still leaks:

• There is a leak at the check valve in the fuel pump: Replace the fuel delivery unit, refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.

Assemble in reverse order of disassembling. Note the following:

• The ignition must be off.

• Open the shut-off valve - B - and drain valve - C - and let the fuel drain into the measuring container before to removing the pressure gauge for the fuel pressure.






- Remove the (VAS 6550) with (VAS 6550/1) and (VAS 6550/2).

- Attach the fuel line so that it clicks into place.

- Press the fuel line on again and pull to make sure the connection is engaged correctly.