1986 Ford F-250 fuel prime loss/ surging

[Bigblocknick]

I’m I need of some help. I have a 1986 Ford F-250 with an 7.3idi in it when running the truck on the front tank I can prime it at the shradder valve and will prime just fine, I will take the truck for a drive it will run ok then it will surge but stay running and when I come to a complete stop the truck will idle rough and shut off but can restart after cranking for 30plus seconds. This problem only happens on the front tank rear tank performs normally. I have recently replaced sending units in both tanks, new selector valve, new mechanical fuel pump and injector return lines. Fuel lines seem to have a good connections no signs of leaking to the naked eye. I have read in another form that a guy had put a electric fuel pump on his truck with a similar issue, would it be beneficial to this issue or is there still a underline problem that will continue.

 

[IDIBRONCO]

Since your truck runs fine on one tank, but not the other, I'd suspect that the fuel selector valve (FSV) is not completely switching and allowing some sir into the fuel system when on your front tank.

 

[riphip]

IF you decide to change to electric (I did), make sure you get a top rated pump & don't cheap out. If the is a leak, it will show up. Yours seems to definitely be sucking air. Do you still have the water separator on the truck in operating order? Have you pulled the ring lately? If so, cram a 3/8" bolt with a smooth shoulder in the drain hose under driver foot board & see if the problem clears up.

 

[Stu Bailey]

Haven't been on in a while and just logged in for the same exact problem. Truck used to suck air when running off the front tank after it was below 3/4 full. I didn't have the time or money for the fix so I have been running her on just the rear tank for about a year with no problems. About three weeks ago I started to get the random surge while driving but never had hard starts or stalls. After about a week or so of the surging I swapped out the fuel filter and has only been downhill since then. Now the truck will start and then shut off after a couple seconds. It then takes about 30 seconds of cranking to purge all the air and get her started again where she then runs perfect. The shradder valve purges pure air during those 30 seconds and then what she starts again its just fuel. I have double checked the filter to make sure it is on right and it is. I have no idea where the air is coming from. But I was thinking that it might be the fuel selector valve, or the sending unit on the rear tank is compromised too like the front. I have access to a vacuum tester, anyone have any thoughts on chunks of line that I should check? Also haven't bled the water separator in a while, I'll probably hit that this weekend with the oil change.

86 F250 6.9

 

[IDIBRONCO]

Hey, nick. I had another thought today. Just to recap for others, in a PM, he told me that the FSV and the shower head are both new. I'm wondering if something didn't quite get sealed perfectly when you replaced the FSV. I'm mostly thinking of the feed line from the front tank. I believe that these fuel lines use an o-ring or something similar to actually seal against the hard fittings like on the FSV. Maybe this is letting a little bit of air into the system while fuel is being drawn through the line from the front tank.

 

[wrecked]

I was gonna say check the connector seals on the tank fittings but I think you just did. There is an o ring in the coupler. I cut the QCs off the rear tank lines after the retainers broke, spliced to a rubber line and gear-clamped it. I can fish a 1/4 inch socket in there just as easily as a slotted screwdriver...

Edit: you can adapt rubber to a plastic line, but it goes without saying to ensure a clean, clean fit. (Use acetone to soften the plastic a little bit to increase the bond) And be careful not to overtighten the clamps. I've done this on a Chevy astro gasser that pushes 65psi from the tank.