Hello all its my first post here and I need some help, that's why I'm here.

I have a 1995 F350 EFI 460 gas and about a month ago I noticed the rear tank would not want to take any gas, I do not see any obstruction.

Just this last weekend after a brief drive I stopped at the gas station, when I opened the rear fuel tank it was pressurized. When the cap came off it was just for lack of better words, under pressure coming out. Never seen anything like that, the front tank did not do this.

What would cause this? Any ideas or replies are much appreciated.

 

The rear tank may be full of fuel and the Fuel Delivery Module in the rear tank may have a bad check valve in it.
Do you use the rear tank?
If the rear tank is not full then the vent tube has slipped down and needs to be pulled back up into place.

 

Thanks subford. Yes I use the rear tank and its not full, I'l have to check for the vent tube.

Any idea about the pressure?

 

I think that would be normal with the tank that you were running on as you pulled to the refueling pumps. You have a check valve in the fuel cap to let air in but not to let the vapors out.
Fuel vapors trapped in the sealed fuel tank are vented through the orificed vapor valve assembly in the top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the carbon canister (located in the engine compartment or along the frame rail) for storage until they are purged to the engine for burning. On a two tank system the vapor line is "T"ed at the front tank.
Fuel vapor in the fuel tank is vented to the carbon canister through two vapor orifice rollover valve assemblies. The valves are mounted in rubber grommets in expansion areas on both sides of the upper surface of the fuel tank. A vapor space between the fuel level and the upper surface of the tank is combined with a small orifice and float shut-off (rollover) valve in the vapor valve assemblies to prevent liquid fuel from passing to the carbon canister. The vapor space also allows for thermal expansion of the fuel.

 

I have a 88F150 4x4 duel tanks. Will not run off the front tank. Have changed front tank, new low pressure pump, primary pump, and deverter valve. When you try to run off front tank, fuel pump has a strong humming noise. Switch back to the rear and noise goes away. Any ideas? Thanks.

 

!988 F150 dual tanks, will run of the back tank only. have replaced deverter valve, front pump, and primary pump. put switch in front and it runs off the back. Help please.

 

Sounds like the front pump is not running.

 

brand new tank and pump. got it at advanced auto. I have a selector switch ordered. Done changed everything else.

 

The Center for Auto Safety, www.autosafety.org/ford-fuel-system-recalls, lists fuel system recalls for Ford going back to the flaming Pinto fiasco. Farther down the page are a couple of entries involving E series vans and F series pickups in the late '80s and early '90s. The text involving the pickups alludes to replacing the o-rings in the "Dual Function Reservoir" which is the euphemism for tank selector valve. Apparantly there was a problem with the compound used in the original o-rings. I have had trouble with my '89 and an '88 we used to have. The owner of the Napa store I normally do business with was quite certain that the DFR had to be purchased from Ford. I surmise the reason is liability concerns due to the recall. There is also a site with pictures of the proceedure to dismantle and reassemble DFR. Even before I found this info I had resolved to tear mine down figuring I had nothing to lose if I ruined it anyway. After all I take my life in my hands driving a rolling molotov cocktail. I intend to contact a local Ford parts department about availability and price.

 

I'm having similar issues. 89 F250 7.5 4x4 runs fine on the front tank but on the rear tank it may run for 1 to 10 minutes then acts like it is running out of fuel reguardless of the quantity of fuel in the rear tank. Flip the switch to the front and it is fine again. I disconnected the line at the slelctor valve and only had a trickle so i replaced the pump and the old kinked plastic lines with rubber lines. With the tank out and the pump assembly in a bucket of fuel I tested again. the pump was working fine but I noticed that sometimes, not always, the fuel would return to the rear tank while running on the front tank and the rear pump shut off. I dissassembled the selector valve and finding no issues other than a little sediment I cleaned, lubricated and reinstalled only to have the same problem. Thinking the diaphram was stuck I switched the lines on the valve so that the rear tank would feed through the same ports as the front had and see if the issue reversed. Still the rear tank is not working. Out of exasperation I installed a new selector valve from motorcraft and still am not able to use the rear tank. The only thing I can think of is the dash switch is intermittent to the rear tank but that is odd and doesn't account for the front tank back feeding the rear. Anyone else have an Idea?

 

Thanks, valentine. I appreciate your input. I was planning to do as you did: clean the selector and replace when(if) I ruined something. I will probably still give it a try. On my daughter's 88 f150 I replaced the in tank pump on the front tank and got it to working again for awhile. Now it exhibits the same symptoms as my 89. If I ever get it figured out I will fix 2 maybe 3 pickups. Please keep us informed.
RF

 

So I added 7 gallons more fuel to the rear tank just to be sure i wasn't having cavitation issues with the rear running at 1/4 full. I only tried to run the rear tank twice after the new selector valve was installed and it didn't take long to quit. So after about a week I gave it another shot and to my surprise the rear tank is running fine. At least for the last 20 miles worth of in town errand running. Air in the lines? Could be there was less fuel in there than the 1/4 tank indicated on the guage. I now have a different issue though. I filled the front tank at the same time as adding fuel to the rear and haven't used any of it yet. When I stopped for lunch today I smelled gas. The front tank is steadily dripping from the pressure letoff valve at the top of the tank. The one that sends the extra fumes to the charcoal canister.
Hopefully this is from splash over and not the rear tank back feeding the front. The question is where to get new valves and grommets and what are they actually called? I can't find them online and my local parts store people are clueless.

 

One thing I note: When I replaced the in-tank pump on the '88 half-ton, I tried the old one too. It seemed to pump fine at first but as I ran it longer it seemed to falter intermittently. This won't solve the selection problem(I don't think it will). I have yet to dig into mine but it needs to happen soon.