Fuel Pressure: Testing and Inspection

Fuel Pressure Regulator And Residual Fuel Pressure, Checking

The fuel pressure regulator maintains fuel pressure relative to the intake manifold pressure.

Requirements
- Fuel Pump (FP) relay OK
- Fuel pump OK
- Air Cleaner (ACL) element OK
- Battery Positive Voltage (B+) OK

- Open fuel filler cap, and close again (to release pressure).


WARNING!
Fire Hazard! The fuel system is under pressure. Before disconnecting fuel lines or opening test connections, cover the connections with a rag to absorb discharged fuel. Carefully release pressure by slowly disconnecting the hose, or by opening the fuel filler cap to release pressure.







- Before opening connection (arrow), cover with rag to prevent fuel spray.







- Install fuel pressure gauge VAG1318 with adapters VAG1318/11 and VAG1318/12 in fuel supply line.


NOTE:
- VAG1318 must be installed with the shut off valve between the gauge and the fuel rail for proper evaluation of residual pressure tests.
- Valve on pressure gauge must be open (lever in direction of flow)


- Start engine and run at idle.
Specified value: approx. 3.6 bar (52 psi)


NOTE: If fuel pressure is not released, check whether fuel supply and fuel return lines have been interchanged.







- Disconnect vacuum hose (arrow) for fuel pressure regulator.
- Fuel pressure must increase to approx. 4.2 bar (61 psi).
- Switch ignition off.
- Check residual pressure by observing pressure reduction.
After 10 minutes at least 3 bar (44 psi) pressure must still be indicated on gauge.

If residual pressure drops below 3.0 bar (44 psi):
- Start engine and stop engine after fuel pressure has built up.
- Close valve on fuel pressure gauge VAG1318.

If residual fuel pressure holds:
- Connection between fuel pressure gauge and fuel pressure regulator leaking.
- Fuel pressure regulator leaking; replace if necessary.
- Fuel injectors leaking. Refer "Fuel injector","Fuel Injection Volume, Fuel Injector Leakage and Spray Pattern, Checking" Testing and Inspection

If residual fuel pressure drops again:
- Connection between fuel pressure gauge and fuel supply line leaking.
- Fuel supply line at fuel tank leaking.
- Check valve in fuel pump leaking.


NOTE: Before disconnecting the fuel pressure gauge, close the valve, disconnect line at VAG1318/12 adapter, and pour left-over fuel into suitable container by opening valve.