ok.so i just bought this truck 2 weeks ago. been a ford man all my life. my mom had a truck like this but 93. and no problems outta it. when i bought the truck he told me both tanks work just was out of gas in the front tank. yeah right. i put 4 gallons in it and it never budged the needle. so i just figured ok bad fuel pump and used the back tank. well truck has been acting funny and sluggish. thought ok.... fuel filter. changed it and no improvment. well i went down and put 10 gallons in my back tank and yeah. when i got home started smelling gas and fuel spewing out my front tank. my question is. can i replace just one fuel filter and it be ok? or am i going to have to buy both pumps?

 

I believe the problem is with a crossover valve thing, not with pumps. (Sorry, I didnt have the issue with my dual tank truck so I never inspected this, and my truck now is a single, so I do not know proper terms.)

 

FYI.. The fuel level sender is a seperate device from the fuel delivery module, so the motor may run just fine on a tank that always shows empty because the level sender is bad. In your case You need to replace the fuel delivery module in the front tank, it contains the check valves that are supposed to prevent this crossflow problem but it sounds like thay have given up. The FDM is a plastic case that also contains the actual fuel pump, and if that one still works I suggest you hang onto it because it sounds like the pump in your rear tank is also failing. The pump itself can be replaced you just have to dismantle the FDM and swap it. And while you are in the front tank replace the fuel level sender.

 

OMT,

I agree with Conanski. I just did this job on my front tank. I have some pictures if you want to see what it looks like. This link should take you there. If it doesnt work, just go to my gallery.
1991 Ford F150 4x2 - Front Fuel Pump Replacement
Hope this helps!

Chris

 

thank you guys for the quick response. I am really hoping that this recall i heard about this issue still covers me! i have changed a couple fuel pumps in my life but is this truck different in the fact that when i go buy that airtex fuel pump is that what i am going to get is just the pump? or is it a full drop in unit like most? i dont really want to tear apart the FDM. i guess what im asking is if the part you buy from autozone a package? is it a new pump,sender,etc all together like most other pumps? and yes the rear pump is failing it has became much louder and the truck takes longer to crank. so if worse comes to worse would i be able to just replace one of the two pumps? i cant afford to drop 300 dollars on two new pumps. especially if im still going to spew liquid gold back onto the ground. thia

 

If you just replace one pump make it the front tank, that way you fix the transfer problem as well. And yes most times the replacement "fuel pumps" are the complete FDM assembly ready to drop in or at least the resovoir portion without the hard line assembly.. which detatches easily.

Here is what the FDM looks like assembled and completely dismantled.

 

wow thank you for that info and pics! here is what i did. the front fuel pump seems to be working. but if i have front tank selected, the fuel guage no workie. so i bought a new FOMOCO sender unit and am going to just try and use the front tank. if i never put gas in the back tank i should be ok right? Im 25 and raising both my teenage sisters. i had 150 bucks to spend on the truck. so i figured i would fix the sending unit issue with the front tank since that pump still works. also how do i find out what gallon size the front tank is? i went with 19 gallon because i knew that was the most common on these trucks. please tell me i was right?

edit. the parts house i went to didnt sell the fuel pump with a new sender unit. i really really wanted to buy both the pump and the sender unit but it was going to be 420 for the FOMOCO piece and the carter pump only was 130 and the FOMOCO sender unit which is what i bought was 160 after tax.

 

There are models that have the 19 gallon front tank, but I dont know exactly which ones. Mine has a 16 gallon front. Ill check my manual after work and look that up. I agree with Conanski, you should fix the front tank first because that will kill two birds with one stone (new pump fixes crossflow, new sender fixes gauge problem). You could just not use the back tank to prevent crossflow, but I would not let any residual fuel sit too long in there. It will go bad and varnish everything in the tank. Its just awful. Look at link I sent you to my gallery. You might try siphoning whatever is in there out or pumping it to the front via crossflow. If you could live without a gas gauge until you have enough for the pump, then you could buy the pump and just change them both at the same time. Its no fun going right back into a tank you just put back up. Ask me how I know that.

Chris

 

thanks HD. but im probably going to be going back in eventually lol. last night i dropped my front tank and changed the sending unit(dont have the cash to afford the whole FDM).... well i got the truck put back together and guage works now in front tank. but after test driving it, the truck dies on me. so i just put it in park, key off then start. started fine and i drove it back home is first to keep the rpms up. same thing today. drive it around runs good. then when i let off the gas to turn or stop. MAJOR hesitation and stalls. if i hit the gas it will keep runnin. what could this be??? i was thinkin my FPR but i dont have any way to check the thing besides pulling the vacuum line. please help sorry for the long post

 

late night bump. i pulled the battery and reset the codes. truck runs better but now it seems like the cross flow problem has reversed it self! my truck is showing 1/2 tank in both tanks now! and i know when i dropped the front tank it was full to the top. i am getting really frustrated now please help me. anybody?

 

That's interesting. I have had that stalling problem you speak of. You might try cleaning the Idle Air Control Valve. Its a valve mounted to the side of the throttle body. Its easy to take off. You take it off and clean it out with some carb cleaner. That valve controls the bypass of intake air around the throttle plates to maintain the proper airflow when you idle or take your foot off the throttle. They plunger in it tends to get carbon'd up.

As far as the FPR, yes pulling the vacuum line and checking for fuel is one thing to do. It sounds as though fuel pressure gauge would help you immensely. It connects to a schrader valve on the fuel rail and shows you the pressures.

As far as the new crossflow issue, I would make sure to verify that the tank is actually taking gas to determine what the next steps should be. Im curious, when you pulled down your front tank, was there a fitting attached to one of the metal lines that come out of the hanger assembly (where the rubber hoses hook up to)? It would look like this.


Hope this helps a little.

Chris

 

no that was not on any of the lines. im assuming that is the check valve ford used to fix this problem. i tried the recall thing and they told me it aint happening on my truck. which pisses me off. and yes the crossflow thing is happening again. my front tank is now at a 1/4 and the rear tank is 3/4. also now when switch to the back tank the fuel pump makes a god awful noise. can i just unplug one of the damn pumps so it quits taking this fuel or pinch the line off somewhere. i mean this is rediculous. im open to all options short of just lighting a rag and throwing it in the cab.

 

You're correct. That is the external check valve ford used to "fix it" instead of changing pumps. I found that my truck had them when I changed the fuel pump. If you had one you might've been able to use it as a band aid temporarily. Oh well.
I'm a bit confused as to whether or not your crossflow has reversed or has begun to backfill to both tanks. With the rear tank backfilling, I take it the front pump does in fact work. To me it sounds like you'll have to change at least one pump. I would probably start with the back pump and move to the front later on since you say that the rear is making a bad noise. I wouldnt trust that front pump to work correctly(not backfill) for too awful long if it's suddenly stopped backfilling. Mechanical problems dont fix themselves.
Unplugging a pump electrical connector won't stop the crossflow. I've read about guys on here wanting to plug the lines. That would work but I'm not sure how to go about it or if they had any success. Hopefully someone else will chime in on that. Sorry I can't offer more help right now. Maybe something will come to me later.

Chris

 

thank you HD for sticking thru this with me! it has been really gettin to me. i am now wondering, I should be able to replace one pump and use that tank exclusively and i it has a good check valve it shouldnt allow fuel to go to the other tank right? i am wanting to replace the front pump. i am thinkin that if i replace it it wont allow fuel to leave the front tank and go to the rear tank. am i right? or am i going to replace the pump and the fuel is going to leave the front tank and go to the rear then i will never get it out of there?

 

No problem, I'm just glad I'm able to help!
Actually, it's the other way around. Whichever tank is backfilling, that tank has the bad pump. So if the rear tank is taking gas, then that pump has the bad internal valve. The intent is that the valves inside the Fuel Delivery Module (pump assembly) prevent reverse fuel flow when the pump is shut off. Here are a couple of pictures:



So whichever one is taking gas, that's the pump that needs replaced. A pump with a bad valve can still pump fine, but it's problem occurs when it is turned off.