Fuel Pressure Regulator and Residual Pressure, Checking

The fuel pressure regulator controls the fuel pressure as a function of the Manifold Absolute Pressure (MAP).

Special tools and equipment

- VAG 1318 pressure gauge

- VAG 1318/6+7 adapter

WARNING!
Fuel system is under pressure! Before opening system, place rags around the connection point. Then release pressure by carefully loosening connection.

Test sequence

I - Engine code ATW
II - Engine codes AUG, AWM

- Open threaded connection (arrow) and catch exiting fuel using a rag.

- Connect VAG 1318 pressure gauge to supply line -1- and fuel distributor using adapters VAG 1318/6 and 1318/7.
- Open shut-off valve of pressure gauge. The lever points in the direction of flow.
- Start engine and let run at idle.
- Measure fuel pressure. Specification: about 3.5 bar positive pressure

- Disconnect vacuum hose from fuel pressure regulator (arrow). Fuel pressure must rise to about 4.0 bar positive pressure.

If specified value is not obtained:
- Check flow quantity of Fuel Pump (FP).

If specified value is obtained:
- Switch ignition off.
- Now check for proper seal and residual pressure. Observe pressure drop on pressure gauge for this. After 10 minutes, there must be at least 2.0 bar positive pressure.

If residual pressure falls below 2 bar positive pressure:
- Start engine and let run at idle.

- Wait until pressure has dropped, and then switch off ignition. Simultaneously close shut-off valve of VAG 1318 pressure gauge (lever perpendicular to direction of flow -arrow-).
- Observe pressure drop on pressure gauge.

If pressure does not drop:
- Test check-valve on Fuel Pump (FP).

If pressure does drop again:
- Check whether pressure gauge is properly sealed.
- Check whether line connections, O-rings in fuel rail, and fuel injectors are properly sealed.

If no leaks are found:
- Replace fuel pressure regulator

NOTE: Before removing pressure gauge, put cleaning rags back around line connection which is to be disconnected.