Fuel Pressure Regulator and Residual Pressure, Checking
Fuel Pressure Regulator and Residual Pressure, Checking
NOTE: Fuel pressure regulator regulates fuel pressure according to intake manifold pressure. This ensures that the pressure drop at the fuel injectors remains the same for each speed and load range of the engine.
Special Tools and Equipment
- VAG1318 with VAG1318/7 adapter, VAG1318/8 pressure hose with connectors and VAG1318/15 adapter
Test requirements:
- Fuel Pump (FP) OK, checking. Testing and Inspection
- Fuel Pump (FP) OK, checking
- Fuel filter OK
- Battery voltage at least 12.7 V
- Vehicles with automatic transmission Selector lever in P or N.
WARNING!
Fuel system is under pressure! Place a cloth around the connection point before opening system. Then release pressure by carefully loosening connection point.
- Remove engine cover (arrows).
Checking system pressure
- Connect VAG1318 pressure gauge using adapters VAG1318/7, /1318/8 pressure hose with connectors and 1318/15 adapter in supply line.
- Disconnect vacuum hose from pressure regulator to intake manifold at pressure regulator and seal line.
NOTE: If fuel should escape at the vacuum connection of the pressure regulator during the following pressure test, replace pressure regulator.
- Start engine and let run at idle.
- Measure fuel pressure.
- Specification: 3.8 to 4.2 bar
- If the specified value is not reached, replace pressure regulator on a trial basis and repeat pressure test.
- If the specified value is not reached again, check Fuel Pump (FP) or supply line for damage (e.g. pinched areas) and replace if necessary.
- If the specified value is exceeded, check return line for damage (e.g. pinched areas) and replace if necessary.
NOTE: During the following test, the engine must not run for an unnecessarily long period of time with the vacuum hose removed. Otherwise, the higher fuel pressure can cause enrichment of the fuel to air ratio, which under some circumstances can cause the oxygen sensor control limits to be exceeded, causing a DTC to be stored.
- Start engine and let run at idle.
- Switch of electrical consumers (A/C system etc.).
- Connect vacuum hose at pressure regulator while observing pressure drop at pressure gauge.
- Fuel pressure must drop by approx. 0.5 bar when connecting the vacuum hose.
If the pressure change does not occur, the following tests must be performed:
- Check vacuum hose for tears and damage.
- Check vacuum hose at intake manifold for throughput by disconnecting from pressure regulator and blowing into it.
- If no leaks can be detected and if the vacuum hose has throughput, replace the pressure regulator.
Checking Residual Pressure
- Residual pressure 10 minutes after switching engine off (minimum pressure).
- Specified value with a cold engine: approx. 2.2 bar
- Specified value with the engine at operating temperature: approx. 3.0 bar
NOTE: Pressure increase for an engine at operating temperature limited by the fuel expansion is normal.
- Start engine and let run at idle.
- Wait until pressure has dropped, and then switch off ignition. Simultaneously close shut- off valve of VAG1318 pressure gauge (lever perpendicular to direction of flow -arrow-).
The following malfunction are possible if the pressure does not drop:
- There is a leak in the threaded connection between the pressure gauge and the fuel supply line
- There is a leak at the supply line at fuel tank.
- There is a leak in the check valve in the Fuel Pump (FP).
NOTE: Pressure gauge displays the pressure behind the stopcock "intake manifold side" after the stopcock is closed (in direction of fuel injector, fuel pressure regulator). If the pressure drops in front of the stopcock (in direction of fuel tank), the device cannot detect it. For this reason, the center of this page states "If the pressure does not drop..".
The following malfunctions are possible if the pressure drops again:
- Fuel pressure regulator faulty
- Fuel injectors not properly sealed
- Threaded connections of pressure gauge behind stopcock is not properly sealed.
NOTE: Close stopcock for removing the pressure gauge, loosen threaded connection at VAG1318/15 adapter and let excess fuel escape into catch reservoir by opening stopcock.