Fuel Pressure Regulator and Residual Pressure, Checking
Fuel Pressure Regulator and Residual Pressure, Checking
Special tools, testers and auxiliary items required
• Pressure Tester (VAS 6550)
• The fuel pressure regulator regulates the fuel pressure to approximately 4 bar.
• The fuel pressure regulator is located on the fuel filter. From October 2005, the fuel pressure regulator is integrated into the fuel filter and cannot be replaced.
• Observe safety precautions. Refer to => [ Safety Precautions ] Multiport Fuel Injection.
• Observe the rules for cleanliness. Refer to => [ Clean Working Conditions ] Multiport Fuel Injection.
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the fuel lines, place a cloth around the connection point. Disconnect the connection carefully to release the pressure.
- Disconnect fuel supply line - 3 -. Press the circlip upward into the housing to release the line - 3 -.
- Connect the (VAS 6550) to the fuel supply line with the (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut off valves are open.
- Start engine and run at idle speed.
• If the engine does not start, activate the fuel pump with output Diagnostic Test Mode (DTM).
- Check the fuel pressure on the (VAS 6550).
• Specified value: 3.7 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:
- 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 October 2005, the fuel pressure regulator is integrated into the fuel filter and cannot be replaced.
- Repeat the test.
If specified value is again not obtained:
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Service and Repair.
If the specified value is not reached, check the residual pressure as follows:
- Watch the pressure decrease on the (VAS 6550).
• After 10 minutes the pressure must not drop below a 3.0 bar decrease.
If the pressure drops further:
- Start engine and run at idle speed.
- Switch the ignition off and close the (VAS 6550) shut off valve - B - immediately.
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 fuel injectors for leaks.
If the pressure drops again:
(Leak on fuel tank side)
- Check the fuel lines for leaks.
If no malfunctions are found in the fuel lines:
- Test the check valve in the fuel pump. 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 Assembly Overview.
• From October 2005, the fuel pressure regulator is integrated into the fuel filter and cannot be replaced.
- Bleed fuel supply system. Refer to => [ Fuel System, Bleeding ] Service and Repair.