Residual Pressure, Checking

WARNING: This page is about a different car, the 2009 Volkswagen GTI and 2008 Volkswagen GTI. However, it is still accessible from the selected car via links, so may be relevant.

The fuel pressure is OK and the pressure tester -VAS 6550- is connected. Checking the fuel pressure, refer to FUEL PRESSURE, CHECKING .

Fig 1: Identifying Pressure Tester VAS 6550 To Fuel Supply Line And Adapters VAS 6550/1 & VAS 6550/2
Courtesy of VOLKSWAGEN UNITED STATES, INC.

Test Sequence

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

-- Check the fuel pressure on the pressure tester.

Specified value: 4.0 to 7.0 bar

-- End the On Board Diagnostic (OBD) and turn off the ignition.

-- Watch the pressure decrease on the pressure tester. 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 lever -B- on the pressure tester as soon as pressure accumulates. The lever is perpendicular to the direction of flow.

Fig 2: Identifying Shutoff Levers

Courtesy of VOLKSWAGEN UNITED STATES, INC.

If Pressure No Longer Drops Now

NOTE:

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

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

If no malfunction can be found:

-- Replace the high pressure pump. Refer to HIGH PRESSURE PUMP .

If the Pressure Drops Again

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

-- Check the fuel line to the fuel filter for leaks.

If no malfunctions are found with the 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.

Fig 3: Identifying Fuel Supply Line At Fuel Filter

Courtesy of VOLKSWAGEN UNITED STATES, INC.

-- Connect the pressure tester -VAS 6550- between the fuel filter and fuel supply line using the hoses -VAS 6550/1- and -VAS 6550/2-.

Fig 4: Identifying Pressure Tester VAS 6550 And Hoses VAS 6550/1 & VAS 6550/2

Courtesy of VOLKSWAGEN UNITED STATES, INC.

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

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

-- Check the fuel pressure on the pressure tester.

Specified value: 4.0 to 7.0 bar

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

Fig 5: Identifying Shutoff Levers

Courtesy of VOLKSWAGEN UNITED STATES, INC.

-- Watch the pressure decrease on the pressure tester. After 10 minutes the pressure must not drop below a 3.0 bar decrease.

If the pressure drops:

-- The pressure retention valve in the fuel pump is faulty, replace the fuel delivery unit. Refer to FUEL DELIVERY UNIT .

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.