I have the same issue many of us are having - fuel pumping from one tank to the other to the point of over-flowing out of the fill cap. I have done exhaustive searching on the internet - including this forum and a couple of other Ford forums. I get conflicting info, or info that doesn't quite match my vehicle exactly. My problem is this: I cannot start my truck with front tank selected. It sputters and sputters. So I start it with rear tank selected. After it starts, I can switch to front and it runs fine. I also have fuel that is transferred from the rear to the front tank, to the point of overflow.
So, after looking around, it appears to be a check valve on the front tank that is bad. Is the check valve located on the outside of the tank, or on the inside with the entire sending unit/pump assembly? FTR, I have a 1996 F150 4x4 4.9 straight 6. FYI I found this, but don't know if this is a '96 or not:
1983 Ford Bronco TSBs & FSAs (Recalls) for '83-96 Broncos & F150s picture | SuperMotors.net
1983 Ford Bronco '90-96 Fuel Pump System picture | SuperMotors.net
Any help is greatly appreciated. TIA!!

 

It is in the fuel delivery module in the tank. In this link it is in the upper left of the diagram

1983 Ford Bronco '90-96 Fuel Pump System picture | SuperMotors.net


With your problem of fuel transferring from rear tank to front you are correct the front check valve is bad

 

Thank you!!! Good and bad news. Now I know where it is, but it looks like I have to take the tank off and replace the sending unit to fix it.

 

Another fix to this is a Checkvalve that fits onto the fuel line. Same endpoint, different means.

Here's a pic of one, it came on my truck and I just kept it. No idea on where to get one.

 

Those external check valves were added as part of a recall. Many have found those also fail.

 

Mine seemed to be working, so I kept it as a "Just in case" thing.

 

Yes, my second link in the original post is a picture of one. While they may fail, it might be easier to install one of those for the time being. Do you think that could be installed without completely removing the front tank? Maybe just loosen it a bit to give me room to reach up there? Within the next few years, I'll be getting a rust-free bed to replace the one I have now. At that time, I can replace all of the innards of the gas tanks. I just need a fix to last a few years.

 

It can be done.

 

Was the check valve attached to the blue (pressure) line, or the gray line?

 

I'm WANTING to say the Blue line (1 line is bigger than the other)

 

I think it was covered, but the answer is: yes

There is one in the FDM and it fails.

In 1991/92 time frame ford issued a broad recall to install check valves on the outside, inline witht he fuel output line - all you had to do was empty one tank, show up low on the other and voila.

Not everyone did this tho, and the recall was even given to second owners.

So, I have not been able to source this part and Ford no longer stocks it. if you can find one in a boneyard: yay, it removes exactly the same way the fuel line does - with a simple $5 tool from advance or whatever.

 

I just did this to my 1993 F250. I dropped both tanks installed the check valves and a new fuel pressure regulator. from what I understand the main issue is the fuel pressure regulator goes and sends high pressure back to the tanks breaking the check valves. Ford has a kit that they used to use but no longer stock. I found one on ebay for $48 shipped.

F4PZ 9155 D Ford 1992 93 F Series 5 0 5 8 7 5L Dual Fuel Filter Kit Recall 93S68 | eBay

looks like they might be sold out but that is where I got it. I just did it this past week but am not sure if it is working or not.

also if your front tank has an aftermarket pump and hanger assy with the pressure line facing backward the check valve might not work as it puts the pressure line kinked against the bed. at least mine did. this kit had all instructions in it as well.

here is the kit for yours
http://www.ebay.com/itm/F4PZ-9155-A-Ford-1990-91-F-SERIES-4-9L-Dual-Fuel-Filter-Kit-for-Recall-93S68-/151076854637?pt=Motors_Car_Truck_Parts_Accessories&hash=item232ce1db6d&vxp=mtr#ht_458wt_1161
to drop the front tank it is two 13mm bolts with 15mm nuts on the side of the tank. the tank will drop some but might not be enough to get the fuel lines off (which you need the tool to do they are cheap. )then you have to take off the filler neck (5/16 Hose clamp) and the tank will drop until the wires are tight. you should have plenty of room then. Hope this helps.

 

Whoa - Thanks much for the link!! I just ordered it. A freind of mine is a mechanic at a Ford dealer and he said the parts dept wanted $250 for the kit. Said they had a hard time finding one, but that was the price. I told him thanks, but no thanks!! He did say it contains a check valve for both tanks, and it looks like this one does too!

 

If you have a way to lift the bed (forklift, shop crane, block and tackle, a couple buddies, whatever) you can just take the bed off and not fuss with the tank mounts at all.

Depends on what looks easier based on condition of the bolts.
The bed bolts sometimes snap if they're real corroded... the tank fasteners do the same.

I always just take the bolts out and prop the bed up with a couple sturdy 2x4's... but I have a Southern truck with my choice of easy-to-remove fasteners.

 

Ugh I hate living in CT. my bed bolts were so rusted I cold not get two of them off with a 1/2 inch air impact gun. I also have an 8' bed and my bolts are carrige bolts with nuts underneath. the tank bolts I was able to get off easily.

that kit comes with two check valves and the fuel pressure regulator gaskets and screws for it. it is the exact ford kit says ford on the box and all.