Fuel Pressure: Testing and Inspection

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.