Fuel Pressure Regulator and Residual Pressure, Checking

Fuel Pressure Regulator and Residual Pressure, Checking

The fuel pressure regulator controls the fuel pressure depending on intake manifold pressure.

Required special tools and test equipment
- Pressure tester VAG 1318
- Adapter 1318/11
- Adapter 1318/12
- Adapter 1318/13

Test requirements
- Fuel pump delivery rate must be OK; checking:

Checking


WARNING!
The fuel system is under pressure! Before loosening hoses or opening the test connection, cover the connection with a rag Only then, open carefully to slowly release pressure


- Open fuel filler cap briefly (release pressure).







- Cover the fuel supply line connection (arrow) to protect against fuel spray.
- Slowly open connection and catch leaking fuel.







- Connect pressure tester VAG 1318 to fuel rail using adapters VAG 1318/11, VAG 1318/12 and VAG 1318/13.


NOTE: The valve on the pressure tester must be open (lever pointing in direction of flow).
- Start engine and let run at idle.
- Measure fuel pressure.
Specified value: approx. 3.5 bar (50 psi)







- Disconnect vacuum hose (arrow) for fuel pressure regulator.
Fuel pressure must increase to approximately 4.0 bar (58 psi)
- Reconnect vacuum hose.
- Switch ignition off.
- Check for residual fuel pressure by monitoring decrease in pressure on gauge. Specified value:
After 10 minutes: at least 2.5 bar (36 psi)

If residual pressure drops below 2.5 bar (36 psi):
- Start engine and let run at idle.
- After pressure has built up, at the same time:
- Switch ignition off.
- Close valve on pressure tester VAG 1318-lever in OFF position (arrow).
- Monitor decrease in pressure on gauge.

If residual pressure still drops below 2.5 bar (36 psi), possible malfunctions are:
- Leaking connection between pressure tester and fuel line
- Leaking connection between fuel supply line and fuel rail
- Faulty check valve in fuel pump; removing and installing:


If residual pressure no longer drops below 2.5 bar (36 psi), the possible malfunctions are:
- Leaking fuel pressure tester connections after shut-off valve.
- Faulty fuel pressure regulator
- Leaking fuel injectors


NOTE: When disconnecting the pressure tester, close the shut-off valve, disconnect adapter VAG 1328/12, then catch excess fuel in a container by opening the shut-off valve.