Fuel Pressure Regulator and Residual Pressure, Checking
Fuel Pressure Regulator and Residual Pressure, Checking
Pressure gauge (VAS 6550)
Perform the following:
• The fuel pump function must be checked. Refer to => [ Function and Voltage Supply, Checking ] Fuel Pump, Checking.
• The fuel pressure regulator regulates the fuel pressure to approximately 4 bar.
• The fuel pressure regulator is located on the fuel filter.
• Follow all Safety Precautions. Refer to => [ Safety Precautions ] Safety Precautions.
• Follow the guidelines for cleanliness. Refer to => [ Clean Working Conditions ] Clean Working Conditions.
Fuel system is under pressure!
• Wear protective goggles and protective clothing in order to avoid injury and contact with the skin.
• Before loosening line connections, place cloths around the connection point. Then release pressure by carefully pulling off the line.
- Disconnect fuel supply line - 1 -. Push the locking ring upward and into the housing.
- Connect the pressure gauge (VAS 6550) to the fuel supply line with the adapter (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut-off valves are open.
- Start the engine and let it run at idle.
• If the engine does not start, activate the fuel pump with output diagnostic test mode.
- Read the fuel pressure.
• Specified value: 3.8 to 4.2 bar
If fuel pressure is OK, check residual pressure.
If the specification is exceeded:
- Check the fuel return line between the fuel filter and the flange for possible restrictions or blockages.
If no malfunction can be found:
- Replace the fuel filter if the fuel pressure regulator is faulty.
If the specification is not obtained:
- Check the fuel lines for possible restrictions (kinks) or blockages.
If no malfunction can be found:
- Replace the fuel filter.
- Repeat the test.
If specified value is again not obtained:
- If the fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit, Removing and Installing ] Service and Repair.
If the specified value is not reached, check the residual pressure as follows:
- Observe the pressure drop on the pressure gauge.
• After 10 minutes the pressure must not drop below a 3.0 bar decrease.
If the pressure drops further:
- Start the engine and let it run at idle.
- Switch on the ignition and immediately close cut-off tap - B - of the pressure tester.
If pressure no longer drops now:
Check for the leak on the engine side. Repeat the residual pressure check. Close the shut-off valve - A - this time to determine if there actually is a leak on the engine side.
- Check the fuel rail and the fuel injectors for leaks.
If the pressure drops again:
(Leak on fuel tank side)
- Check fuel lines for leaks.
If no malfunctions are found in the fuel lines:
- Check Fuel Pump (FP) check-valve => [ Fuel Pump Check Valve, Checking ] Fuel Pump, Checking.
If no malfunction is found here either:
- Replace the fuel filter.
- Fuel System, Bleeding. Refer to => [ Fuel System, Bleeding ] Service and Repair.