First thanks, this site has been awesome to getting my 77 ford 250 working, a weird problem recently happened.

First I believe 'aux' tank is my front one, and 'main' is my back, simply based on the gauges when I filled them. Anyway, so I topped them both off and drove around, a day later I see my back (main?) tank leaking, I open the gas cap and it is FULL. It was dripping bad, I collected easily about half a gallon, and thats not including what leaked in the night. When I switched tanks, this would slowly go down, but as soon as I swap tanks again, this starts to fill back up.

Somehow it seems this tank is getting full, how does the fuel system work, ever hear of this problem? Thanks tons.

 

What's happening when you switch tanks, there are 2 valves that are suppose to move. Apparently, only the supply side is switching when you switch tanks allowing the return fuel to go into the wrong tank. The return line is sending all the fuel into the main tank regardless which tank it's pulling from. I would start by checking the electrical connections to it. I had a 97 that would not switch unless I tapped the switching valves by hand. My truck it was located under the drivers side door inside the frame.

 

It shouldn't be able to do that, if it's factory - I don't think they had return lines on the ones that age - at least none of mine do. Has somebody added an electric pump, or a return line from the carb, etc? They should just have 1 solenoid valve under there, with 3 ports - 2 "in"s, one from each tank, and 1 "out", to the fuel pump, and it should be under suction. Do both tanks seem to work? Where is the truck from originally? If it was an emissions one, they had some weird vent and vacuum lines, might be something there, fuel getting routed backwards down a vent line from the carb to the rear tank, or something of the sort. Not sure though, never worked on a Cali Ford of that era.....

 

I would say it is the tank selection valve. One way to test this is to pull the lines from the valve, block off the midship tank (side) and run the aft tank (rear) straight to the fuel pump. What it sounds like is the valve isn't completed shutting the aft tank off when selecting the midship tank, therefore causing fuel to go into the aft tank.

 

Oooh, is your front tank behind the seat? Then absolutely, that would make perfect sense it's the selector valve - it's leaking past internally, and gravity-flowing from the high one to the low one. I was thinking the front tank was under the bed too, and it would have to be getting pumped uphill.

 

Hey guys thanks for all the answers. My 'front' tank is in the middle of the truck, its not substantially higher than the back so not sure it would be gravity. The strangest, is the truck was parked level, and it was spilling out of the TOP of the gas tank fill, implying that there was some pressure or something (truck was off) because this was higher than any other part of the tanks.

 

My 1990 F250 4wd did that and continued to even after the Ford recall replaced the transfer valve. That valve goes bad and pumps from one tank to the other. My solution was to drive on the tank that overflowed first, then switch to the other one. It was easy, didn't fixed the problem except it no longer overflowed and ended my frustration.


My first Ford was a 59 Ranchero. 67 Mustang, 72 Econoline, 72 Pinto, 75 F100, 78 Econoline, 82 F150, 85 nF250, 88 Fi50, 89 Bronco, 90 F250, 2002 Ranger XL


Drove the 90 F250 over 300,000 until it got pretty tired. I've always done all my own work, maintenance etc. Surprising the things you pick up along the way. Such as the 2002 Ranger Automatic trans not shifting when a turn signal bulb went out. Lots of integrated circuits in that one.

 

On my FR250, the transfer switch was replaced by a Ford recall. But that didn't correct the problem. The valve continued to pump gas into the forward tank from the rear one. I had to drive the gas from the from tank first, then go to the rear tank. It eliminated the spillage problem, so I left it at that.

 

If you lave a late model 77 NON high boy there for a low boy and have factory tanks, you should have only one elec controlled valve located in front of the aft fuel tank. See pic. That could be the issue.

78/79 duel fuel tanks frame switch-Duralast/Universal 3 port fuel selector valve used with SW48 toggle switch Part Number: FSV4

If you have a manual fuel switch in the cab on the floor beside the seat, well that is a different story.

Do you have all the emissions stuff on your truck? Do you have a vent line coming out the top of your rear tank and running down the passenger side of the frame going to 2 white square or a 1 round frame mounter charcoal filter canisters?

There are two differences between the tanks. Tanks with EEC have a hole in the top center of the tank. A rubber grommet and check valve are pressed into the hole. A line goes from the check valve along the inside of the passenger side frame rail to the engine compartment where it hooks up to a charcoal canister. Non-EEC tanks don't have this hole. The other difference is the nipple for the breather line that is located right next to the nipple for the filler hose is located 180 degrees opposite.
If you are going from an EEC tank to a non-EEC tank you must also change the fuel cap to a vented style. The EEC tanks are vented through the EEC system and use a sealed fuel cap. Non-EEC tanks vent through the fuel filler cap.
If you run a non-EEC tank and a sealed cap the minimum is you'll have fuel starvation problems, at worst a collapsed fuel tank.

 

I am in need of some help. I bought a 95 F 250 5.8 gas 5 speed manual with 97k original miles. I have had her about 5 months. She ran very strong up until about a month ago. I noticed she started to loose power and chatter when trying to accelerate. I parked fof a couple days. I did tune-up (plugs, wires, cap, rotor.) I figured make it run a lot better because looked like all original. Took the truck on a run and fuel low so I switched the tanks (which I had never done before because previous owner told me something was wrong with the front tank, so I would just use the rear.) I ran it like that for a few seconds until it started running terrible. So I immediately switched it back. It continued to run bad and even die at times. I noticed that the fuel was being used faster than normal. When I got home I found the fuel dumping from the charcoal canister and the filler tube of the front tank. I took off one of the vaccum lines from the box and took off the fuel cap from the from and it quit dumping out of the canister but it still came out the filler tube of the front tank. Please advise on this situation. Thank you very much.


Stephen Boyett

 

Please ask questions in the 1987/96 F150 and larger truck forum. This is the 1973/79 F100 and larger truck forum.