1991 f150 5.0 fuel tank problems one tank will sifle gas to the other tank and run out the overflowow can you repair it your self?

If I'm not badly mistaken, there was a recall on that problem.

I'd google the problem first, and then contact a dealership and ask about it.

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That recall ended in 2001. You need to replace the fuel pump in the tank that is filling up. ie: If back tank is pumping into front tank and overflowing it then the front tank fuel pump module is bad. Replace it. Part is between 138.00 and 200.00 at a parts store.