1991 F150 overflowing rear tank
 

I have a 1991 F150 and the rear tank keeps overflowing. It looks like there is gas being pumped from the front tank into the rear. I have a 5.0L V8 and what I have read in the forums is that my issue is probably with the tank selector valve. Looking at my specific truck it doesnt seem to have one of these. The fuel lines just come together in a T fitting. Is there any other possible location?? Thanks

If your truck does not have a selector valve, it has a shuttle valve in the Fuel Delivery Module in each tank. This is essentially a pilot-operated check valve which allows fuel to return to the tank only when the pump for that tank is running. If the rear tank is overflowing the shuttle valve for the rear FDM is stuck open. AFAIK the shuttle valve is not available as a service part, you will need to replace the entire FDM.

Read this caption:

https://www.supermotors.net/getfile/...lcrossflow.jpg

...and stay hungry. ;)

I was gonna say, I thought there was a recall... my dad's 1990 F-250 (now by brothers) has the switch tanks

The sad part is that the truck was originaly taken to the local Ford dealership here in Tustin (CA) and given a completely different diagnosis. Pretty bad. I read in the recal that it expires in 2003.. is there anyway to still take advantage of it?? I thought safety recalls never expire??

Hey SMF, I have a 95 that is doing the same thing. I had replaced the front tank fuel pump, and now wish I had done the rear tank too. I just run off the rear tank till almost empty, run off the front tank till almost empty, altho the front tank drains quicker as gas is running to the rear tank because the rear tank fuel pump shuttle valve is faulty. Sooner or later I'll work up the courage to tackle the rear tank fuel pump. Good luck.

Some safety recalls don't expire, and some do. If you can't get the recall valves (which weren't much better than the originals), you'll have to replace the FDM. Read these captions:

https://www.supermotors.net/getfile/...mbnail/j-3.jpg

BTW
How did the dealership diagnose it?

The dealership said it had a bad TPS and canister purge valve. After my own diagnosis i found the charcoal canister to be bad due to fuel being forced through it after the tank overflowed. After the charcoal canister filled with fuel it was pumped into the intake causing all sorts of issues.

BTW Steve83 thanks for all the help, those links are great!!

It looks like the ford dealer has the check valve available, it costs about 3$. They also talked about replacing a regulator? As well as a fuel tube connector assembly costing 173$??? Seems like i should only need the check valve, but i want to make sure as its a good amount of work to drop the tank.

Filling the charcoal canister with gas doesn't hurt it - it just prevents it from working until it gets purged through normal driving. Gas leaking into the intake makes the engine run rich, and can wash the oil off the rings resulting in cylinder scoring & low compression if allowed to continue, but if that didn't happen, stopping the leak should eliminate all those symptoms. It sounds like your real problem is an ineffective vapor/rollover valve in the rear tank.

What's the PN of the $3 check valve? Find out exactly what regulator & connector they want to replace, and why.

Instead of dropping the tank, consider lifting the bed. Read these captions:

https://www.supermotors.net/getfile/...ail/165rim.jpg

While riding with my friend Robert about 12 years ago, we took a load of junk to the dump using his '88 F-150 (Custom, with Posi-Trac rear end and a 302 that WILL NOT die) with dual tanks. As soon as we got there, the old man said "Hey your back tank is spilling over..."

We looked at each other and started throwing s#]> out left and right so we could get outta there!

We high-tailed it north on 78 back to his house, gas spewing out the whole way there. My comment about two miles before the exit was..."well, I hope no one throws a cigarette out or we are done for...." We laugh at that story to this day, but if there HAD been a cigarette tossed between Holly Springs and Byhalia the story might have ended differently.

That said, AFAIR, his selector valve had to be replaced and that truck still running Ford Tough.

*double post sorry*

It ended up being the in-tank fuel pump that was causing the problems on his '88...

Last time I was at ford the check valve was over 100 bucks and needed to be special ordered. What is your part number?

Adrianspeeder

As usual, SMF, Steve83 is right. Taking the bed off is probably easier than dropping the tank. And unless you are lucky enough to have a hoist like he does, make sure you call 2-3 of your friends over. Those beds are not light. Good luck and keep us posted.