Fuel Pressure Regulator and Residual Pressure, Checking

Fuel Pressure Regulator and Holding Pressure, Checking:

The fuel pressure regulator maintains and regulates the fuel pressure at a value that depends upon intake manifold pressure.

WARNING: Fuel will be expelled. To help prevent fuel spray when loosening connections, wrap a cloth around the connection.

Fuel Pump delivery rate OK.






- Remove fuel rail test connection plug -1- and connect VAG 1318 pressure gauge with VAG 1318/1 adapter to fuel rail. The pressure gauge valve must be closed (lever -arrow- at right angle to direction of flow).
- Start engine and run at idle.
- Read fuel pressure on gauge.

Specification: approx. 3.5 bar (50 psi)






- Disconnect vacuum hose from fuel pressure regulator on upper intake manifold (arrow).
Fuel pressure must increase to approx. 4.0 bar (58 psi).

- Switch ignition OFF.
- Check for leaks and holding pressure by watching pressure decrease on gauge.
- After 10 minutes, residual pressure should be at least 2.5 bar (36 psi).

If pressure drops below 2.5 bar (36 psi):

- Start engine and run at idle.
- After normal system pressure has built-up, at the same time
- Switch ignition OFF
- Clamp-off fuel return line with blue markings at fuel rail
- Watch pressure decrease on gauge.

- If pressure does NOT go down:
Replace Fuel pressure regulator.

- If the pressure does go down:

Check Fuel pump check-valve.

Check for leaks:
Fuel line and hose connections
0-rings on fuel rail
Fuel injectors (N30 - N33, N83, N84).

- Check pressure gauge for leaks.

CAUTION: Before disconnecting the pressure gauge, hold a container over the connection and release fuel pressure by opening the pressure gauge valve.