i have a 94 f150 302 that i have stopped driving and at wits end trying to fix. when i was driving it there was a strong oder of gas coming into the cab and it looked like someone had poured gas into the vapor canister. i don't know why it is damp and wet in there so i wanted to remove it and just let the rubber hose just hang there but didn't do it as of yet. i also have a duel gas tanks on it. could not figure out why it seems like the rear tank runs out of gas faster than the front so i went looking for a gas leak and did not find one and wanted to try and figure out what the gas mileage would be but didn't know how to do that either. i know that trucks of the early 90's don't have good gas mileage but wanted to keep it and try to fix it before i totally give up on it and drive it into the ocean. the truck has been sitting on the street in front of my place for the last 6 or 7 months. the truck does still have the factory 10 hole aluminum rims on it and all i did was change the tire size to a 275/60/15 rear and s245/60/15 front bfg's by changing the tire size would it have a big change in gas consumption. is there a chance the gas mileage could be improved. any info on this is appreciated

 

its a return style fuel system, so the unused fuel from the back tank dumps back into the front tank

 

Sounds like you have the really common fuel crossover proble. If the rear tank runs out of fuel faster it means it is pumping the return fuel into the front tank. Likely the front tank is overfilling and the fuel is being pushed up the vapor vent line into the charcoal canister. The FDM in one of the tanks needs to be replaced, but I don't remember which one is the problem, the pumping tank on the non-pumping tank. Someone else can clear that up.

 

The fuel should return to the same tank it is pumped from. The check valve on the non-selected fuel pump assembly is supposed to be stopping the fuel from entering the non-selected tank.

Often, I have heard of both fuel pump assemblies (fuel delivery modules) developing check valve problems, and sometimes replacing one does not fix it. You may end up needing to replace both. That is the best long term recommendation. But you can start by replacing the one first and see how it does.

Once you get the fuel transferring problem fixed, then re-calculate the mileage. Some of your fuel is currently ending up in the other tank, or overflowing, so the mileage calculations are not accurate at the moment.

Get the fuel out of the charcoal canister before reconnecting the canister, or it will make the truck run poorly due to the extra fuel the computer does not realize is being added from the canister overflowing. The canister is designed for vapor only, not liquid. I would first try letting the fuel evaporate from the canister, but you may have to blow it out with some air pressure. Be very careful. Replace the canister with a junkyard unit if it ends up being easier, it will at least be safer than messing with air pressure and liquid fuel spraying out.

 

thanks for all the positive feed back guys............hey babarche where is the check valve on the fuel system is it attached to the fuel pump or fuel module or is it external somewhere on the fuel return line.........don't know anything about the ford fuel system on these trucks.........need to know where to start looking........

 

The check valve is part of the fuel pump module. When they first had the cross flow problems, there was a recall, and check valves were installed in the line outside the tank, between the lines off the top of the tank and the line that connects to the tank. So if your truck was ever serviced for the recall, it may have an external check valve. In my experience, the external check valves didn't always fix the problem, and eventually the true fix was to replace the fuel pump module and remove the recall check valve.

Best bet is to replace the fuel pump module that is allowing fuel to flow into the tank when the other tank is selected.

 

hey babarche......i will look into replacing the fuel pump assembly and possible both and find out how much it will be and i am the 2nd owner of this truck so i will also be looking to see if there is an external check valve........hope i know what it looks like.......thanks for the response........wish me luck.................

 

I found a photo of an external check valve (it is connected to the fuel line coming out of the tank on the right): Thanks to subford for the picture.

The entire fuel pump assembly is around $150, more if you but one from a dealer. Some people have had luck using an additive in the fuel like Berryman's B-12 or Marvel Mystery Oil to free up a stuck check valve, but it may still need to be replaced if that doesn't work.

 

I had the same thing happen to my 96 w/dual tanks. I had to replace the fuel pump in the front tank to fix it. I paid a lot to have it done, and in hindsight, wish I hadn't. It isn't that hard to do it yourself as long as the tank is empty. The hardest part is getting the fuel lines off. You need to buy the "good" fuel line seperation tool if you do it.

 

hey babarche, thanks for finding that photo it was very helpful. thanks subford for the picture. i didn't find the external check valve on the truck today. so i am assuming its the front fuel pump assembly or (module) that will need replacing. i will look on ebay or somewhere else for the part that is needed. any help on finding this part other than ebay please let me know.............thanks a lot for your help, and all the positive feed back from everyone..............