Fuel Pressure In Engine/Motor Compartment, Checking
The residual pressure in the low fuel pressure system is checked with the Vehicle Diagnostic Tester.
Select repair group 20 - Fuel Supply System on the Vehicle Diagnostic Tester and follow the instructions.
Only the necessary preliminary work and the connecting of testing equipment are described in the repair information.
The appropriate Service Information will specify which steps are necessary.
The required tools are named in the procedure and are listed above in the tool list.
Special tools and workshop equipment required
- Pressure Tester Kit:VAS 6550
- Pressure Tester Kit - Adapter Set:VAS 6550/3
- Vehicle Diagnostic Tester
Connecting the testers:
The fuel system is under pressure.
Risk of injury from fuel spraying out.
- Wear protective eyewear.
- Wear safety gloves.
- Reduce the pressure: place clean cloths around the connection point and carefully open the connection point.
-- Remove the fuel supply line from the high pressure pump. Refer to OVERVIEW - HIGH PRESSURE PUMP . Disconnect the connector couplings. Refer to CONNECTOR COUPLINGS, DISCONNECTING .
-- Collect leaking fuel with a cleaning cloth.
Vehicles with fuel supply lines without connector couplings on the high pressure pump:
-- Connect the Pressure Tester Kit - Adapter Set - Fitting:VAS 6550/3-1 -3- from the Pressure Tester Kit - Adapter Set:VAS 6550/3 to the fuel supply line -1-.
-- Secure the connection with a hose clamp -2-.
-- Connect the Pressure Tester Kit - Hose 2:VAS 6550/2 -4- to the Pressure Tester Kit - Adapter Set - Fitting:VAS 6550/3-1 -3-.
-- Connect the Pressure Tester Kit - Hose 2:VAS 6550/2 -2- to the connection -A- on the Pressure Tester Kit:VAS 6550 -1-.
-- Connect the Pressure Tester Kit - Adapter Set - Hose 2:VAS 6550/3-2 to the connection -B- on the Pressure Tester Kit:VAS 6550 .
-- Connect the Pressure Tester Kit - Adapter Set - Hose 2:VAS 6550/3-2 to the high pressure pump and secure with a hose clamp.
Vehicles with connector couplings on the fuel supply lines to the high pressure pump:
-- Connect the fuel supply line -2- to the connection -A- from the Pressure Tester Kit:VAS 6550 -1-.
-- Connect the connection -B- from the Pressure Tester Kit:VAS 6550 with the Pressure Tester Kit - Hose 2:VAS 6550/2 to the high pressure pump.
Continuation for All Vehicles:
-- Make sure all connected lines are securely in place by pulling on them.
-- Make sure the drain valves -A- through -C- are sealed on the Pressure Tester Kit -1-.
Risk of a fire due to leaking fuel.
Severe injuries and burns are possible.
- Before the test, check if all connected lines are securely connected by pulling on them.
- Remove any cleaning cloths soaked in fuel from the vehicle area.
-- Follow the instructions on the Vehicle Diagnostic Tester.
Searching for leaks on the fuel tank side:
-- Check all of the fuel lines for leaks and damage.
Searching for leaks on the engine side:
-- If there is a leak on the engine-side, check the fuel pipes and high pressure pump for leaks.
-- If no malfunction is found, check the fuel injectors for leaks. To do this, remove the spark plugs and check through the spark plug hole to see if a fuel has collected on the piston crown due to a leaking fuel injector.
To prevent the fuel pump from activating, disconnect the battery before removing the Fuel Tester Kit:VAS 6550 . Refer to BATTERY, DISCONNECTING AND CONNECTING .
Reduce the pressure in the system before removing the connector couplings. To do this, hold the drain hose at connection -C- in a suitable container. Then carefully open the shut-off valve.