Fuel Pressure Regulator and Residual Pressure, Checking
Fuel Pressure Regulator and Residual Pressure, Checking
• Follow all safety precautions. Refer to => [ Safety Precautions ] Multiport Fuel Injection.
• Pay attention to the rules of cleanliness. Refer to => [ Clean Working Conditions ] Multiport Fuel Injection.
Special tools, testers and auxiliary items required
• Pressure Tester (VAS 6550)
• 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. From 10.05, the fuel pressure regulator is integrated in the fuel filter and cannot be replaced separately.
• Follow all safety precautions. Refer to => [ Safety Precautions ] Multiport Fuel Injection.
• Pay attention to the rules of cleanliness. Refer to => [ Clean Working Conditions ] Multiport Fuel Injection.
The fuel system is under pressure!
• Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin.
• Before loosening line connections, place a cloth around the connection point. Then release pressure by carefully pulling off the line.
- Disconnect the fuel supply line - 3 -. Press the circlip upward into the housing to release the line - 3 -.
- Connect the pressure tester (VAS 6550) to the fuel supply line using the adapter hoses (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut off levers are open.
- Start the engine and run at idle speed.
• If the engine does not start, activate the fuel pump with the output diagnostic test mode.
- Check the fuel pressure on the pressure tester.
• Specified value: 3.8 to 4.2 bar
If the fuel pressure is OK, check the residual pressure.
If the Specification is Exceeded:
- Check the fuel return line between the fuel filter and the flange for possible restrictions (kinks) or blockages.
If no malfunction can be found:
- The fuel pressure regulator is faulty. Replace it.
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 pressure regulator.
• From 10.05, the fuel pressure regulator is integrated into the fuel filter and cannot be replaced separately.
- Repeat the test.
If the Specification is Again Not Obtained:
- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Service and Repair.
If the specification is not reached, check the residual pressure as follows:
- 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:
- Start the engine and run at idle speed.
- Turn the ignition off and close the pressure tester shut off lever - B - immediately.
If the Pressure No Longer Drops Now:
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 rail and fuel injectors for leaks.
If the Pressure Drops Again:
The leak is on the fuel tank side.
- Check the fuel lines for leaks.
If no malfunctions are found in the fuel lines:
- Test the fuel pump check valve. Refer to => [ Fuel Pump Check Valve, Checking ] Fuel Pump, Checking.
If no malfunction is found here either:
- Replace the fuel pressure regulator => [ (Item 5) Fuel Pressure Regulator ] Fuel Filter Overview.
• From 10.05, the fuel pressure regulator is integrated in the fuel filter and cannot be replaced separately.
- Bleed the fuel supply system. Refer to => [ Fuel System, Bleeding ] Service and Repair.