9 - Air In Fuel System Test

9. Air in Fuel System Test





Purpose:
To determine if air is being drawn into the fuel system.










Recommended Procedure:
- Remove the rubber hose and clamps from the fuel return line at the fuel filter.
- Install a clear line from the return line to the fuel filter. Loop the excess line at a point higher than the filter.
- Observe the fuel in the line while the engine is running. The fuel should be flowing toward the return line to the tank. After approximately 5 minutes of running, fuel flow should be free of air.
- If the fuel is foamy, check the fuel supply lines from the tank to the fuel pump for an air leak.
- If there is no fuel return flow, remove fuel regulator block. Use care not to lose or damage O-ring as it must be used during fuel regulator block reinstallation. Inspect fuel return orifice screen for debris. Clean as necessary.

NOTE: If the filter has just been changed, air may be present in the clear line until purged from the system.

Possible Causes:
Loose and leaking fuel line fittings at:
- fuel tanks
- selector valve
- connection between the selector valve and engine
- O-ring connection from chassis line to engine fuel inlet tube
- hose clamps, rubber line on fuel pump

Tools Required:
Clear line and hose clamps