Fuel Pressure: Testing and Inspection

Fuel Pressure Regulator And Holding Pressure, Checking

Special tools and equipment required







- V.A.G 1318 with V.A.G 1318/6 and V.A.G 1318/7

Conditions
- Fuel pump relay OK
- Fuel pump OK
- Fuel filter OK
- Battery voltage at least 11 V
- Vehicles with automatic transmission: Selector lever in P or N position

NOTE: The fuel pressure regulator regulates the fuel pressure according to intake manifold pressure.


WARNING: 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 pulling off the hose or cap.


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






- Open union (arrow) and catch escaping fuel with a cloth.
- Connect pressure tester V.A.G 1318 with adapters V.A.G 1318/6 and 1318/7 between supply line and fuel rail.
- Open cut-off valve on pressure gauge (valve handle points in direction of flow).
- Start engine and run at idling speed.
- Measure fuel pressure.
Specification: approx. 3.5 bar







- Pull vacuum hose (arrow) off fuel pressure regulator.

NOTE: If fuel flows out at the vacuum connection on the fuel pressure regulator during the following pressure test, install a new fuel pressure regulator.

Fuel pressure should increase to approx. 4.0 bar.

If specification is not obtained:
- Install a new pressure regulator as a trial measure and repeat pressure test.
- If fuel pressure still does not match specification, check fuel pump and supply line for damage (e.g. pinching) and replace if necessary.

If specification is obtained:
- Reconnect vacuum hose.
- Switch off ignition.
- Observe pressure drop on pressure gauge to check leakage and holding pressure.

After 10 minutes the pressure should still be at least 3 bar.


If the holding pressure drops below 3.0 bar:
- Start engine and run at idling speed.







- Switch ignition off after pressure has built up. Simultaneously close cutoff valve on pressure gauge V.A.G 1318 (valve handle at 90 5 to direction of flow).
- Observe pressure drop on gauge.

If the pressure drops again, the following faults are possible:
- Unions on pressure gauge downstream of cut-off valve leaking
- Fuel pressure regulator faulty
- Injectors leaking

If the pressure does not drop, the following faults are possible:
- Union between pressure gauge and fuel supply line leaking
- Supply line leaking at fuel tank
- Non-return valve in fuel pump leaking.