Just call me Sean

iTrader: (1)

The tank selector switch has separate contacts for the pump and gauge. Just because the gauge switches doesn't mean the pump is.

AppleTech

Good point. I did have a listen with the truck running and don't hear both running (can hear them switch).

toothman

my 1990 4.9l dual tank system had the same cross over symptom. The front tank was filling from the rear tank. The rear pump had been replaced 15 yrs. ago. The front tank pump was the original 1990 ( replaced 2021)........the check valve WAS hard to find. However here is the part # for the check valve.......1L3Z9J274BA

Steve83

You're replying to a thread that has been dead for 10 years. And that check valve is NOT necessary with any replacement FDM - it was only for the factory (failure-prone) FDMs. So no one needs it now - not even you. That's why it's hard-to-find.

arch713

I understand this is an old post. But this is still an issue. How are the tanks not in use over filling? Through the supply line or the return line? I thought it was a check valve I. The return side not working, it must be the supply line pressurizing and sending gas to the tank not operating