E-150 '92 Unique Fuel Problem

[CFreds]

Van drives fine until fuel level gets somewhere below 3/8 of a tank. Then it starts missfiring and losing power. If ignored, it gets to the point where it will barely idle. Limping to a filling station and filling up, it instantaneouly is fine again. Has anyone seen this? Any suggestions?
Thanks in advance

[moonjohn]

Sounds like a problem that I once had.
You are starving the engine for fuel.
You have a plugged line in your fuel breather system.
As the fuel goes down in the fuel tank, it creates a vacuum.
The fuel pump then can no longer pump the fuel.
Test by pulling over and opening and closing the gas cap.
I solved the problem on my car by leaving the gas cap loose.
Of course this may cause your engine service light to come on if you leave your gas cap loose.