Can not find the air leak. Help?

[pwjackson]

Okay I have made a few post on here about my truck with air getting into the fuel. Here is the run down. Its an 86 F250 4x4 with 125,000 miles. I have put a new IP, lift pump, return caps, cap o-rings, return lines, and new seals on the steel line from lift pump to filter base. We have a clear hose at the back of the intake where the return lines come together and we are still getting air bubbles in the fuel and its makeing it start hard and smoke heavy grey smoke. I also have a clear line hooked up to the lift pump inlet and stuck into a bucket of diesel and no bubbles there. Is there anything I am missing? Where else could I be getting air into the fuel? I getting warn thin as I have not had my truck running correct since June.

 

[Brimmstone]

check the lines where they hit the switching valve and at the tank itself. Mine turned out to be the o-rings in the lines went bad. I just ran rubber fuel line from the sending unit to the switching valve. Problem solved.

 

[pwjackson]

I wish it was that easy but I can rule out anything with the tanks or from the lift pump back because I am running a fuel line out of a 5 gal bucket straight to the lift pump. It is a clear line and I have no bubbles there so the leak must be after the lift pump and before where all the return lines come together at the back of the motor. water seperator has been bypassed also.

 

[franklin2]

A guy I work with discovered his problem was the drain being loose on the bottom of the fuel filter. I would also make sure all the seals on the filter are good and the guts of the shrader valve on the filter boss is tight.

P.S. I am assuming yours is like my 89 7.3. I know the earlier engines may be different but not sure when they changed it around. I believe they have some sort of seperator on the firewall that gives lots of problems on the early engines?.

 

[pwjackson]

Mine is an 86 6.9 it has not been converted to the 7.3 fuel filter.

 

[hesutton]

It sounds like you have a real tough one. My best advice would be to look for any signs of fuel anywhere in the system. Are there any wet spots on the in the caps or lines. Wet spots at the filter head/ filter, schraider valve on the filter head, the return block at the driver's rear on top of the enigine, anywhere on the fuel lines (feed or return), the tank switch valve. Does it do this with a full tank of fuel or only with about a 1/4 tank of fuel?

Heath

 

[pwjackson]

No signs of fuel leaks thats the kicker. Could an injector be bad and allowing compression back through the injector? I would think the engine would have a bad miss if that was happening but it runs and idles great once you get it started.