Fuel System Operation and Tests
AIR IN FUEL TEST
NOTE: Illustration shows in-line injection pump. Rotary
pump is similar.
Air in the fuel system will make the engine hard to start,
run rough, misfire or produce low power. Additionally, it
can cause excessive smoke and knocking.
Whenever the fuel system is opened for repair, it must be
bled to remove any air that has entered the system.
1. Disconnect hose from end of fuel leak-off line
assembly. Connect a hose to end of leak-off line
assembly and place opposite end of hose in a suitable
container filled with fuel as shown.
2. Operate engine and check for air bubbles in container.
If bubbles are present, bleed the fuel system and
repeat test. (See BLEED THE FUEL SYSTEM in this
3. If bubbles are still present, check the following:
Check for loose fuel fittings from the suction side of the
fuel supply pump to the fuel tank to inckude all lines
Check fuel tank suction tube (if equipped) and welded
joints for cracks or holes.
Perform any necessary repairs, bleed fuel system and