New to FTE, was hoping first post wouldn't be about a problem but here we are!
Truck = 1996, F350, Standard cab, 2wd, 460, Auto, 115,000 miles.

Problem = when both (factory installed) tanks are full and I use the front first until empty and then go to the rear tank, the rear tank (16 gallon I think) will go about 70 miles before running empty and some how transferring 1/2 a tank of gas to the front tank. If I fill both and run the rear tank first, it will pressurize the front tank so bad that gas will seep out the front gas cap and if you open the cap gas will come spewing out of the filler neck for a couple of seconds.
It sounds like a tank separator valve issue to me, but I have looked all over the frame rails and can't find anything but lots of fuel line + 1-fuel filter (that I'll be replacing today, now that I just bought the tool to disconnect it).
If this isn't enough of a pain just about a week ago (on a 98+ deg. day) it stalled a couple times at lights, seemed to be lacking in power, had a heavy gas smell under the hood (but couldn't find a leak) and was acting like it was vapor locking. When it was doing this, I would switch from one tank to the other with little to know difference noticed.

F.Y.I. the fuel gauge is working correctly and so does the in-cab tank selector switch.

I had tried searching the forum for this issue, but didn't find any info on where the H*ll a separator valve would be located or what it looks like.

I need your help badly on this, because this truck has to be back together tonight and ready to pull my business trailer by 5:30 tomorrow morning!

 

You have a FDM (fuel delivery module) problem in the front tank.. The check valve seems to be stuck open...

 

Does anyone happen to have a part number for this fuel delivery module?

 

I would suggest checking rockauto-dot-com or your local auto parts store.. (Hint: look under fuel pump)

You will need to get the part number for YOUR application, as the are NOT all the same....

 

You are correct on this, O'Reily had no idea as to which of the 12 listed it was. But they also showed that it has a stand alone tank separator valve!
I'm in the process of pulling the front tank right now!

 

Would the stuck open valve make it to were the fuel rail bleeder won't have fuel pressure after the motor is shut off? While the motor is idling, I have 35#'s (with the vacuum still hooked up to the Reg.) of pressure.

 

I guess I am going to have to pull the tank as well. LMC, Broncograveyard, etc. don't really make it clear what could be causing this.

My project truck is a 1988 F-250 7.5L if anyone has any advice.

Thanks

 

The above info does NOT include your 1988 model, it has a different fuel system......................

The later models had a high pressure pump in each tank, with check valves and other items, all in the tanks... No pump or valves on the frame rail, only thing on the frame rail was the filter and it covered both tanks.

Yours should have low pressure pumps in the tanks, with a high pressure pump on the drivers side frame rail, there should also be a "switcher" valve close to the high pressure pump.

 

Mine is pulled out but can't really tell anything from looking at it, so just plan on replacing it.

 

Just replaced the filter on the frame and the fuel that came out of it was BROWN. I'm going to pull the rear tank to make sure it doesn't have dirt in it, since the front tank looked real clean. I'll probably change out the pump system in the back tank too since I'll have it pulled down.

 

Thanks for that info. I was afraid you were going to tell me my fuel system was somehow more complicated .

I'm planning to just live with if it for now. Unfortunately it is way down on my priority list.

 

Truck Parts and Truck Accessories

Sorry to hijack the thread. I believe the part that i'm needing is #26 the fuel selector valve. Pretty pricey at $210 from LMC.

 

No Problem!! We're all just trying to keep these Beasts ALIVE!

 

Actually I think you need this: