Residual Pressure, Checking

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

Fig 1: Connecting Pressure Tester VAS 6550 To Fuel Supply Line Using Adapters VAS 6550/1 And VAS 6550/2
Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

Test Sequence:

-- Activate the fuel pump with output diagnostic test mode to build fuel pressure.

-- Check the fuel pressure on the pressure tester.

Specified value: 4.0 to 7.0 bar

-- End the output diagnostic test mode 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 diagnostic test mode 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 Drain Valve -C- Is Closed And Shut Off Valves -A And B- Are Open

Courtesy of VOLKSWAGEN GROUP OF AMERICA, 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 the high pressure pump for leaks.

If no malfunction can be found:

-- Replace the high pressure pump. Refer to HIGH SIDE FUEL PRESSURE, RELEASING .

If the pressure drops again:

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

-- Check the fuel line leading to the 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.

Fig 3: Fuel Supply Line At Fuel Filter

Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.

-- Using the hoses VAS 6550/1 and VAS 6550/2, connect the pressure tester VAS 6550 between the fuel filter and fuel supply line.

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 GROUP OF AMERICA, INC.

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

-- Activate the fuel pump with output diagnostic test mode to build fuel pressure.

-- Check the fuel pressure on the pressure gauge.

Specified value: 4.0 to 7.0 bar

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

Fig 5: Identifying Drain Valve -C- Is Closed And Shut Off Valves -A And B- Are Open

Courtesy of VOLKSWAGEN GROUP OF AMERICA, 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.