Gas overflowing please help
FTE Legend
Joined: Jun 2006
Posts: 31,930
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From: Ottawa, Ontario
Do both tanks work? It sounds like the classic fuel transfer problem that can occur whether the second tank works or not, but if the pump in that tank doesn't work there is no way to empty the tank so it will quickly fill and overflow.
Lead Driver
Joined: Feb 2013
Posts: 5,006
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From: Roseville, MN
Quick and dirty solution to the problem Conanski describes is to run the problem tank (rear in your case) first. Then when you switch to the front tank you'll have room for the gas that transfers back to it.
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Tuned
Joined: Apr 2018
Posts: 277
Likes: 1
I can run my truck on the rear tank I had no idea this was a problem until now and had this truck for 3 years
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Tuned
Joined: Apr 2018
Posts: 277
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I'll try that next time I go to town thank you for your help I hope this solves the problem
Hotshot
Joined: Jun 2015
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The solution is to replace the fuel delivery module ( pump assembly). I believe Nothing Special was suggesting that as a work around for the defective check valve.
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Tuned
Joined: Apr 2018
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Do you know where I can find one? I still question why this truck does this but my 85 6.9 idi with dual tanks doesn't have this issue
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Lead Driver
Joined: Feb 2013
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From: Roseville, MN
Wen did Ford switch to the "newer" FDM system? I know there was a different system in the 80s and sometime before the mid-90s they had switched to the FDMs with no separate switching valve. He's running a '91 which is in my gray zone. I don't know if that would be the earlier or later system.
Hotshot
Joined: Jun 2015
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Hotshot
Joined: Nov 2017
Posts: 17,465
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From: Northern Ontario
I have the same problem with mine (‘96 F250 5.8 - I’m pretty sure the systems are basically the same) This is what I figured out.
There is a check valve at each fuel sending unit.
When the fwd tank is selected the fwd tank check valve opens, and the aft check valve closes, allowing the fuel to return to the front only. And vice versa when the aft tank is selected.
There is only one return fuel line from the engine to a splitter, splits off to each tank Sending unit. The return fuel can flow to one or both tanks if a check valve is stuck open. It’s also possible, from what I understand, to have both stuck.
The return fuel is going to the wrong tank, and it will overflow the tank not selected.
The check valve is not repairable.
Im in the process of rebuilding my truck and changing both sending units. For the past year, I’ve been running the aft tank down, then run the fwd tank, then switch back the aft and run it down from the fuel being returned to the wrong tank if I forget, the aft tank will overflow.
There is a check valve at each fuel sending unit.
When the fwd tank is selected the fwd tank check valve opens, and the aft check valve closes, allowing the fuel to return to the front only. And vice versa when the aft tank is selected.
There is only one return fuel line from the engine to a splitter, splits off to each tank Sending unit. The return fuel can flow to one or both tanks if a check valve is stuck open. It’s also possible, from what I understand, to have both stuck.
The return fuel is going to the wrong tank, and it will overflow the tank not selected.
The check valve is not repairable.
Im in the process of rebuilding my truck and changing both sending units. For the past year, I’ve been running the aft tank down, then run the fwd tank, then switch back the aft and run it down from the fuel being returned to the wrong tank if I forget, the aft tank will overflow.
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