Fuel Pressure: Testing and Inspection

Fuel Pressure Regulator and Residual Pressure, Checking
The fuel pressure regulator controls the fuel pressure as a function of the Manifold Absolute Pressure (MAP).







The specified value for this test is dependent on the working pressure of the Fuel Pump (FP). This is about 3.0 bar positive pressure

Special tools and equipment
- VAG1318 pressure gauge
- VAG1318/17 adapter
- VAG1921 hose clip pliers

Test requirement
- Capacity of transfer Fuel Pump (FP) must be OK:

Test sequence
- Remove fuse no. 18 for the Fuel Pump (FP) from fuse holder.


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







- Disconnect coupling of fuel supply line -1- (black or black markings) and catch exiting fuel using a rag.







- Connect VAG1318 pressure gauge to supply line and hose for fuel rail using adapters VAG1318/9 and 1318/17.
- Open shut-off valve of pressure gauge. The lever points in the direction of flow.
- Insert fuse no. 18 for the Fuel Pump (FP) in the fuse holder.
- Start engine and let run at idle.
- Measure fuel pressure. Specification: about 2.5 bar positive pressure







- Disconnect vacuum hose from fuel pressure regulator (arrow). Fuel pressure should rise to about 3.0 bar positive pressurize.

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 at least 2.0 bar over pressure should still be present.

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

If the Fuel Pump (FP) has built up pressure again:







- Wait until pressure has dropped, and then switch off ignition. Simultaneously close shut-off valve of VAG1318 pressure gauge (lever perpendicular to direction of flow -arrow-).
- Observe pressure drop on pressure gauge again.

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

If pressure drops 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:
- Switch ignition off.
- Replace fuel pressure regulator

When removing pressure gauge after completed test:
- Hold a rag over the adapter being loosened and remove pressure gauge.