Fuel Pressure, Regulator and Residual Fuel Pressure, Checking
Fuel Pressure, Fuel Pressure Regulator And Residual Fuel Pressure, Checking
The fuel pressure regulator controls the fuel pressure depending on intake manifold pressure.
WARNING!
Fire hazard! Do not smoke, work near heaters or open flame, or have anything nearby that could ignite fuel. The fuel system is under pressure. Before opening, cover connections with a rag, and open carefully to release pressure.
Required special tools and test equipment
- Pressure tester VAG1318
- Adapter 1318/7
- Adapter 1318/10
- Adapter 1318/13
Test requirements
- Fuel pump delivery rate OK; checking:
Checking
- Connect pressure tester VAG1318 between fuel supply line and fuel rail using adapters 1318/7, 1318/10 and 1318/13.
NOTE: Shut-off valve of pressure tester must be open (lever parallel to direction of flow).
- Remove vacuum line from fuel pressure regulator (to intake manifold) and block line (using VW3093).
NOTE: For the following test, do not let the engine run unnecessarily with the vacuum hose removed, since the higher fuel pressure causes enrichment of the fuel air mixture. The richer mixture could exceed the O2S control limits and therefore cause a DTC to be stored.
- Switch off all electrical consumers (rear defrost, A/C etc.).
- Start engine and let idle.
NOTE: If, during the following pressure test, fuel leaks from the vacuum connection of the fuel pressure regulator, replace the fuel pressure regulator.
- Measure fuel pressure.
Specified value: approx. 3.8-4.2 bar (55.1- 60.9 psi)
If the specified value is not attained:
- Replace fuel pressure regulator and repeat pressure test.
If the specified value is still not obtained:
- Check fuel pump or supply line for damage (e.g. pinched locations); replace if necessary.
If the specified value is exceeded:
- Check return line for damage (e.g. pinch locations); replace if necessary.
- Install vacuum hose on fuel pressure regulator and check for pressure drop on gauge.
Specification: when vacuum hose is installed, fuel pressure must drop by about 0.5 bar (7 psi).
If pressure does not change, the following tests should be conducted:
- Check vacuum line for leaks (cracks, damage).
- Check vacuum line at intake hose for obstruction; remove hose at fuel pressure regulator and blow into it.
If there is no leak and vacuum connection has no obstruction:
- Replace fuel pressure regulator.
Checking residual pressure
- Check residual pressure 10 minutes after shutting oft engine.
- Cold engine (min.): approx. 2.2 bar (31.9 psi)
- Warm engine (min.): approx. 3.0 bar (43.5 psi)
NOTE: The higher pressure with a warm engine, caused by fuel expansion, is normal.
If the specified value is not attained:
- Start engine and, after fuel pressure has increased, switch ignition off.
- Close shut off valve on VAG1318 pressure tester.
If the residual pressure drops (is lower than spec.) again, the following malfunctions are possible:
- Connections for the pressure gauge and fuel lines leaking
- Pre-feed line on fuel reservoir leaking
- Check valve in the electric fuel pump malfunctioning
If retaining pressure does not drop, the following malfunctions are possible:
- Malfunctioning fuel pressure regulator
- Injectors leaking
- Connections for the pressure gauge leaking behind shut-off valve
NOTE: To remove the pressure gauge, close the shut-off valve, loosen the connection on the VAG13181/12 adapter and drain excess fuel by opening the shut-off valve into collector container.