Front Gear Train
This test checks for air leaks in the fuel supply lines. If all components are functioning properly, the fuel lines after
the lift pump will always have a positive pressure. Any poor connections in lines will result in an external leak and
not air in the fuel.
NOTE: This tool does not have an orifice and will result in maximum fuel flow from the lift pump. This will cause
maximum fuel inlet vacuum and will make air leaks and inlet restriction easier to identify.
Disconnect the fuel inlet supply line from the fuel pump.
Install a clear hose and male quick disconnect fitting, Part Number 4918433, into the supply line. Place the other end
of the hose into a bucket or similar container.
NOTE: This test is performed with the engine not operating.
The lift pump can be temporarily activated by turning the keyswitch to the “on” position and by “bumping” the
starter, without staring the engine. The lift pump will operate for 25 seconds.
Look for air bubbles in the fuel as it fills the bucket or similar container.
If air continues to bubble through the clear hose for several minutes, than an air leak is present.
The source to the leak may be in the stand-pipes located in the fuel tank. Refer to the OEM service information for
related information.
Rear Gear Train
Install an M10 CompuchekTM fitting, Part Number 3824842, in the fuel filter inlet diagnostic test port.
Install a 1.09 mm [0.043 in] orificed diagnostic test line, Part Number 3164621, onto the CompuchekTM fitting.
Place the other end of the test line in a bucket or similar container capable of holding approximately 19 liters [5
gallons].
Start the engine and operate from idle to high idle several times to purge the air introduced while installing the
diagnostic fuel line.
Operate the engine at idle and observe the fuel flow exiting the diagnostic fuel line.
If air continues to bubble through the hose for several minutes, then a leak is present.
