How/why does fuel transfer from front tank to rear tank ? I put 6 gallons in front, drove about 5 miles, parked over night, all fuel now in rear tank which was empty. Any ideas????

 

More info: 1987 2.9L FI ext. cab dual fuel tanks

 

I’ve had some posts about my truck running good one day, stalling out, letting it sit, and then it will fire right up and run like nothing ever happened for a while.
I suspect it’s a fuel issue, so I was thinking it was a fuel pump problem. I know the previous owner, so I asked him if he ever had issues with fuel, and he said yes, he said it siphons from one take to the other, so you don’t ever want to run one tank empty. I did a search in the threads, and there was a thread from back in 2004, and it looked like it was related to tank switching valve, but it never really said if that fixed the problem or not. I thought maybe other people have run into this and have found that the valve is the problem. I was ready to pull the box off and switch out all the fuel pumps/sending units, so any info on this “tank siphoning” problem would be greatly appreciated.

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Old 03-07-2011, 09:59 AM



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it's most likely the fuel tank selector valve. look underneath on the drivers side frame rail a little north of the front tank and you'll see a round and square black thing about the size of a fist with 4 lines running toward the rear and 2 running to the front. That's the valve and there's a 99% chance that's your problem. it's pretty common. i had the same issue with mine, replaced it, and i've been fine since.


__________________
1986 F-150 XLT Lariat 4x4. Shortbed, 5.0, AOD, Limitied Slip rear, EFI, dual tanks, A/C (Still R-12)

 

My first post is a cut and paste from a guy with an F-150 & having the same problem as you.

Looks like the tank selector valve is your problem.

BTW, I have the exact same truck as you an 87 2.9 dual tank with a 5 speed manual trans. The 2.9 & the manual trans is an XLNT combination and a kick to drive.

It would be a terrible waste of a good engine if it had a slugomatic behind it.

 

I had a 85 F150 that was doing the same thing. My truck had a diverter valve in between the front and rear tank, inside the frame rail, and it was directly below the left rear wheel housinf.

 

Thanks guys for the advice . It turns out it is a gummed up tank selector valve. I guess the selector valves were turds during this era according to our resident parts guru, NumberDummy.