air in fuel

[jim_22]

OK, seems like a classic problem. I have a 1994 7.3 IDI with Banks Turbo. At high RPM, above 2000, the fuelfilter light comes on and the truck surges like it is starving for fuel (it is, of course). The filter is NEW (the newer one piece type). When I remove the filter, I see it is bubbling with air. So where does it come from? Nothing obvious like hoses, etc. My understanding it could be the lift pump, the shrader valve, the tank pickup, or probably many other things. What to do next? Any help is appreciated.

 

[icanfixall]

How full are your tanks... Some or most tank suctions break off and they pull air at around 1/4 tank... The lift pump does fail but do a flow test before throwing parts at the truck. Others will chime in with how much fuel in how many seconds...

 

[jim_22]

I run veggie oil in the front tank-- but not in the winter. I keep the back tank low on diesel so it does not go old. So yes, it has been way below a quarter tank, but yesterday I put 10 gallons in it and the problem did not go away. Maybe now that I have fuel in there I need to get the air out of the filter and try again? It starts OK but not great. It runs OK through the first 3 gears then in 4th gear the light comes on and it loses power. If I keep on it and take it to 5th at 60-70 mph it feels like it tries to straighten out but never quite does. When I gear down the light goes out and it smoothes out. I acts JUST like a clogged fuel filter but I changed it twice. i suppose it really could still be a clogged filter from some bad fuel before I filled up, but I did change the filter twice. Change it again now that I refueled? Any suggestions welcome.

 

[RLDSL]

If your fuel selector valve isn't functioning perfectly it can also be a point of air intrusion . Mine is about to go in the bin and get replaced with manual valves after it folded about a month after installation
It'll suck air in the forward tank position now for no reason ( and I did extensive testing to eliminate all variables )

 

[jim_22]

yes, I thought of this too, basically everywhere there is a connection. But how to diagnose? Tomorrow I will run on the front tank and see what happens.

 

[gonecrazyi]

Mine started to do this right before the life pump gave out. I was running wvo and the temps dropped really quickly. The truck would surge and act like it was starving of fuel. I ended up running on what the IP could pull one its own, I couldnt get above 35 mph.

I had to replace the filter, and lift pump, as well as remove the lines and blow out all the wvo crap that built up in the lines. The stuff acted like a valve and would allow me to prime the truck but as soon as I started the motor the fuel line would close off and Id run out of fuel.

 

[typ4]

veggie oil will collapse the original rubber hoses and cause this exact problem.

 

[jim_22]

Biodiesel yes, straight canola no.

 

[jim_22]

Just to follow up on my own post, the problem was the mechanical lift pump. Had a new one put in and it runs great on both tanks. Looking back at my records, it seems that the pump was starting to give me trouble a long time ago as the truck will still run with a tired fuel pump.