Fuel Pressure, Checking

WARNING: This page is about a different variant/trim than selected.

NOTE:

The output Diagnostic Test Mode (DTM) activates the fuel pump.

WARNING:

The fuel supply line is under pressure. Always wear protective eye-wear and protective clothing to prevent injuries and fuel from coming in contact with your skin. Wrap a cloth around the connection before removing a fuel hose. Remove the hose connection carefully to release the pressure.

-- Disconnect the supply line (metal coupling) -arrow- and wipe up any leaking fuel with a cloth.

Fig 1: Disconnecting Supply Line And Catch Escaping Fuel Using Rag

Courtesy of VOLKSWAGEN UNITED STATES, INC.

NOTE:

Press the locking ring to unlock the fuel line.

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

Fig 2: Connecting Pressure Tester VAS 6550 To Fuel Supply Line Using Hoses VAS 6550/1 And VAS 6550/2

Courtesy of VOLKSWAGEN UNITED STATES, INC.

-- Make sure the drain is closed and the shutoff 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

If fuel pressure is OK, check the residual pressure. Refer to RESIDUAL PRESSURE, CHECKING .

If the specification is exceeded:

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

If no malfunction can be found:

-- Replace the fuel filter, the pressure relief valve inside the fuel filter is faulty.

If the specification is not obtained:

-- Check the fuel pressure before the fuel filter as follows:

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

Fig 3: 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: Connecting Pressure Tester VAS 6550 Between Fuel Filter And Fuel Supply Line Using Hoses VAS 6550/1 And VAS 6550/2

Courtesy of VOLKSWAGEN UNITED STATES, INC.

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

Fig 5: Identifying Shutoff Levers

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-- Turn on the ignition and actuate the fuel pump using the output DTM.

-- Close the shutoff lever -A- while the fuel pump is running. Pressure must increase to a min. 7.0 bar. If 7.0 bar is reached, open the shutoff lever again immediately!

If the pressure has increased:

-- Replace the fuel filter, the fuel pump is OK but the pressure relief valve in the fuel filter is faulty.

If the pressure does not increase:

-- Replace the fuel delivery unit, the fuel pump is faulty. Refer to FUEL DELIVERY UNIT .