Truck trouble! Pulling my hair out!

My Dads 1991 F150 has always pumped gas from front to rear. Before you ask, the check valve on the pressure line is A-OK. With the tank out, the truck was running with the check valve on the main line and the return stopped off. In that confige it would go about 200 miles + - on a front tank fill.

With the return open, when the truck is running gas will come out of it at a GOOD clip. There is NO valve or switching mechanizm telling the return where to go. IF the front tank return was a problem, why did it run fine with the back tank out and the lines closed off?

We put a new fuel pump in the rear tank, because it wouldn't run on the rear anymore. We put the rear tank back in today, and I had him put in only 3-4 gallons to see if it would run on the rear. It would not.

With a full front tank, at 76 miles on the odo, it ran out of gas. It was all in the rear tank. We have a diagram of the rear tank, and from what I can tell, the wiring is correct. MAYBE not.

But the main question is why is all of the gas so hell bent on getting to the rear tank?

Like I said in the title : /ubbthreads/images/graemlins/Christo_pull_hair.gif /ubbthreads/images/graemlins/Christo_pull_hair.gif /ubbthreads/images/graemlins/Christo_pull_hair.gif /ubbthreads/images/graemlins/Christo_pull_hair.gif /ubbthreads/images/graemlins/Christo_pull_hair.gif

iirc there is a recall on this.
might want to check on it.

He said he'll try to get Ford to do something. He wants to get me settled down, as I'm about to blow up!

I had the same exact thing happen to me on a 91 f250 I had.
I rememebr there was a low pressure pump in each tank and a high pressure pump on the rail by the driver seat.

I don't remember if we fixed it or traded it in like that. I got rid of it back in 97-98. I do remember the gas from the rear pumping to the front tank though.....
Go to fordtruckworld and post it in the pre section. I am sure the guys will help you out. There is a lot of knowledge there.
F150online is another good place with knowledge..
Good luck

Well, a bandaid for the problem was discovered.

The wiring to the pump was backwards. It will run on it now, so at least it wont overun (unless he isn't paying attencion!)

Glad you got it semi figured out....

Tell him to check that site out though. There are a ton of FoMoCo guys on that site. They should know the product well enough to get some ideas when things go wrong...