Air in Fuel (006-003)
B3.9 and B5.9 Series Engines
Section 6 - Injectors and Fuel Lines - Group 06
The MW, A, and P fuel injection pumps equipped with the
engine-side fuel drain arrangement create a self-bleeding
system for air introduced during replacement of the supply-
For faster air purge, small amounts of air can be bled from
the pump by operating the hand primer on the fuel transfer
pump or by cranking the engine.
A source that is often overlooked for air to enter the fuel
system is between the inlet of the prefilter and the suction
tube in the tank. Fuel tanks that have the outlet fitting at the
top have a suction tube that extends to the bottom of the
tank. Cracks or pin holes in the weld that join the tube to
the fitting can let air enter the fuel system.
Keep hands and body parts away from the high-pressure
fuel lines. Fuel coming from the high-pressure fuel lines
are under extreme pressure and can cause serious in-
jury by penetrating the skin.
Check for air in the high-pressure lines by loosening the
fittings at the head. Crank the engine to allow entrapped air
to bleed from the line. Tighten the fittings.
Do not bleed the fuel system on a hot engine; this can
cause fuel to spill onto a hot exhaust manifold, which
can cause a fire.
Operate the engine, and vent one line at a time until the
engine runs smoothly.