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, and once stabilized only slight traces of air should be seen in the line.
- If the fuel is foamy, check the fuel supply lines from the tank to the lift pump for an air leak.

NOTE: If the filter has just been changed air may be present in the clear line until vented.



POSSIBLE CAUSES
Loose and leaking fuel line fittings at:
- fuel tanks
- transfer valve
- connection between the transfer 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