Fuel System Pressure and Residual Pressure, Checking

System Pressure, Fuel Pressure Regulator And Residual Pressure, Checking


NOTE: Fuel pressure regulator regulates fuel pressure according to in take manifold pressure. This ensures that the pressure drop at the fuel injectors remains the same for each speed and load range of the engine.


Special Tools and Equipment







- VAG1318
- V.A.G 1318 with V.A.G 1318/11 adapter, VAG 1318/12 pressure hose with connectors and V.A.G 1318/13 adapter

Test requirements:
- Fuel Pump (FP) relay OK;
- Fuel Pump (FP) OK, checking:
- Fuel filter OK
- Battery voltage at least 12.7 V
- Vehicles with automatic transmission Selector lever in P or N.

Checking system pressure
- Open fuel filler flap briefly (pressure release).







- Remove engine cover (arrows).


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







- Open threaded connection (arrow) and catch exiting fuel using a rag.
- Connect VAG1318 pressure gauge in supply line using adapters 1318/11,1318/12 and 1318/13.







- 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 at fuel pressure regulator.
- Fuel pressure must rise to about 4.0 bar positive pressure.
- Switch ignition off.
- Check for proper seal and residual pressure by observing pressure drop on pressure gauge.
- After 10 minutes, there must be at least 2.5 bar positive pressure

If residual pressure sinks below 2.5 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 VAG1318 pressure gauge (lever perpendicular to direction of flow -arrow-).
- Observe pressure drop on pressure gauge.

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

If pressure drops again:
- Open shut-off valve of pressure gauge. The lever points in the direction of flow.
- Start engine and let run at idle.
- Wait until pressure has dropped, and then switch off ignition. Simultaneously clamp return line (with blue marking) completely closed.

If pressure does not drop now:
- Replace fuel pressure regulator

If pressure drops again:
- Check wire connections, O-rings at fuel distributor and fuel injectors for proper seal.
- Check whether pressure gauge is properly sealed.


NOTE: Before disconnecting pressure gauge, release pressure by opening shut-off valve. Hold a container in front of connection for this.