Air problem but only when running

[bennettj007]

I know that he air intrusion problem has been absolutely beat to death, but I am at a loss on this one. The truck is a 1992 f250 7.3 idi non turbo, auto. Started the truck after sitting for several months and the good news was it fired right up. The bad was the after driving for around 10 miles the fuel filter/pressure light comes on. I get the truck home and start to troubleshoot. I figure a fuel pump or filter so I replace both. The pump is electric and the old filter looked fine. The problem continued and I noticed that the filter was filling with air when running. The funny thing is that the truck can sit for however long and will start and run fine. I haven't noticed any air intrusion problems while sitting but only when running. I started eliminating possible air leaks, new fuel hose from pump by tank all the way to old metal line that ran from filter to mech pump. I eliminated the tank switch and everything, just straight hose to check. Still air in filter. Drop tank and find split in rubber pick up, pull that and put a piece of hose on there to see if that was my air source during suction. Still air in filter. No debris in tank and everything looked good on that end.

I am thinking of switching it back to a mech pump but doubt that could help at all. I have ordered a return line kit to install but without the common start and stall problem I just don't know if that is the air issue. I am thinking about replacing orings and seals on the filter/separator but I am just at a loss. It just seems strange that is will start and run fine no matter how long it sits but then starts getting air and starved for fuel only when driving. The pump has been replaced and seems to be moving plenty of fuel and I think the starving just comes when too much air builds up in the filter and the injection pump starts sucking air. I can bleed the sharade valve when it does this and the truck will again start right back up until it starts to suck more air and fill the filter with air instead of fuel.

So what do you think? Return line leak? Check ball or seals on the filter housing? Or just dump some gas on it and set it ablaze? I am interested to hear opinions. I have used oil burners for info on past problems when I first bought the truck 5 years ago such as replacing the return lines and glowplugs etc.

 

[Agnem]

It's not inconceivable that your electric fuel pump (not sure what kind you have of course) has a seal problem, and could be the part that is introducing air. A simple temporary piece of clear vinyl tubing right after the pump would confirm or deny that.

 

[bennettj007]

I thought of that but dismissed it since I replaced the pump. I will throw a piece of clear tubing on it with a loop to try to catch it pushing air in the top of the loop. Just seemed different then any air problems I have experience. I fought be hard starting and air leaks when I first bought the truck but since then it had not had any issues for years. I even left it sitting for over a year and when out and started it right up after charging the batteries ( a rough sounding start but still firing after 2 seconds of cranking). I just had to post because I could not even find something with search that fit what it was doing.

 

[Thefarmboy21]

I am really interested in this! Mine is doing basically the same thing...mine won't even start off the key, it has to be pull started and purges tons of air at the Schrader valve and basically runs the filter dry. Mine has a mechanical pump with a hose from the tank directly to the pump totally bypassing the rest. I'm fed up! I'm considering taking every single hose off the truck and running all clear to try and find it, I just don't know what to get to withstand the diesel fuel???

 

[mjs2011]

I think you can use just basic clear poly for your troubleshooting, just don't leave it on there long. Or give McMastercarr.com a look, sort play tuning for diesel fuel, I bet they have something.

Sent from my SCH-I605 using Tapatalk

 

[OLDBULL8]

Could it be you didn't cut a V in the bottom of the tank hose you replaced, the pump will suck the hose to the bottom and cut off fuel, the IP will pump the filter dry, that turns the filter light ON. If that's the case, put a brass tee on the hose in the tank.

 

[bennettj007]

I don't think that would be the issue because I have unhooked the line from the pump and flowed over five gallons from the tank while using the pump and hose for a pick up. I was pretty careful to cut it short enough and at an angle when I did it. I am picking up clear hose today so I can get a better look at what it is doing.

 

[icanfixall]

My educated guess is you have a leaky line BEFORE the electrical lift pump. There is no way any air can enter the lines after the pump because of the pressure involved. Where did you install this electrical pump. That also might be an issue.