Fuel Pressure Regulator and Holding Pressure, Checking

Fuel Pressure Regulator And Holding Pressure, Checking

Test conditions
- Fuel pump relay OK
- Fuel pump OK
- Fuel filter OK
- Battery voltage at least 11 volts

NOTE: Fuel pressure regulator regulates fuel pressure as a function of intake pressure.

CAUTION: The fuel system is pressurized! Before loosening hose connections or opening the test connection (to measure fuel pressure), place a cloth around the connection. Then release pressure by carefully loosening the connection.

- Briefly open fuel tank filler cap (to release pressure).
- Cover pressurized screw connection with a cloth.







- Open screw connection -arrow- and catch escaping fuel in a cloth.







- Install pressure measuring device VAG 1318 together with adapters VAG 1318/6, 1318/7 between feed line and fuel manifold tube.
- Open cut-off valve on pressure gauge. Lever points in direction of flow.

NOTE: The shut-off cock of the pressure measuring device should be open (lever facing in the direction of flow).

- Start engine and run at idling speed.
- Measure fuel pressure.
Specified value: approx. 3.5 bar






- Disconnect vacuum hose -arrow- from fuel pressure regulator.

NOTE: Replace pressure regulator if fuel emerges at the vacuum connection of the pressure regulator in the course of the following pressure test.

The fuel pressure should rise to approx. 4.0 bar.

If specification is not attained:

- Replace pressure controller as a test and repeat pressure test.
- If specification is still not attained, check fuel pump/feed pipe for damage (e.g. crushing) and replace, if necessary.

If specified value is attained:

- Reconnect vacuum hose.
- Switch ignition off.
- Test for leaks and holding pressure by watching pressure drop on gauge.
After 10 minutes the remaining pressure should be at least 3 bar.
If the holding pressure drops below 3.0 bar:
Start engine and run at idling speed.







- Allow pressure to build up, then switch off ignition. At same time close cut-off valve on pressure gauge VAG 1318 (valve lever at right angles to direction of flow).
- Observe pressure drop on gauge.

If the pressure drops again, the following malfunctions are possible:

- Unions on pressure gauge after cut-off valve leaking
- Fuel pressure regulator faulty
- Injectors leaking

If the pressure does not drop, the following malfunctions are possible:

- Union between pressure gauge and fuel supply line leaking
- Supply line leaking at fuel tank
- Non-return valve in fuel pump leaking.