Need Help with tank problem
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Elder User
Joined: Jan 2004
Posts: 803
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From: Bobcaygeon Ont.
Need Help with tank problem
My dad has a 91 F150 with dual tanks. For some darn reason the fuel from the rear tank pumps into the front tank and gas pours out the front tanks filler neck. I knoe they had a recall for some special check valves the go on the tank outlets. We replaced them with new ones and it still does the same thing. Is it possible to reverse the lines. I put a new sending unit in the rear tank just this problem started. I would think if you reversed the lines the truck wouldn't run correctly. Is one line larger than the other? Want to make sure i'm going in the right direction before i drop the rear tank again. Any help would be appreciated. Oh ya, there is no valve on the frame to change tanks. They just hook together at a y connector! 
Senior User
Joined: Sep 2003
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From: York, PA
tank problem
Lancer, If I remember correctly, there is three different setups for the fuel tanks in F-trucks, if you got your fuel pump from the aftermarket, you may want to get in touch with your local Ford dealer on the correct fuel pump that you just installed, I just went through this with another customer that installed there own fuel pumps, Airtex fuelpumps explained the difference to me, has to do with check valves in the fuelpump units themselves, some aftermarket companies don't have the right listing and they also don't use check valves in the pumps to prevent flow back through the pump, I am pretty sure it is in the fuelpump. Broken Wire
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Elder User
Joined: Jan 2004
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From: Bobcaygeon Ont.
Broken Wire thanks alot for your reply!! I wonder if you can tell me something. Ford had a recall on my dads truck. It was for a check valve that goes on the sending unit. It is about 2" long. We went to the dealer and they said this was mostlikely the problem. It cost my dad $152.00 for a new set of valves. After changing them we still have the same prob. Do you think we may have got a faulty valve. Also i was wondering if the return line to the rear tank maybe plugged. What do you think. Thanks a lot for the help and hope i might return the favour sometime!! Lancer 
Senior User
Joined: Sep 2003
Posts: 223
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From: York, PA
Lancer, I have no clue what these valves look like, all that I can tell you is that the last phone call I got from another shop about fuel flowing back into the other tank was they installed the wrong pumps in the tank, Airtex did not say anything about going to Ford for check valves, they said the valves where built into the pump preventing backflow back through the pump. So I would say that if the valves that you got from Ford are on correctly, they go inline with fuel flow on the output fuel line and would stop fuel from flowing back through the pump when the pumps are switched from one tank to the other. Am I correct on this? I don't think you have a faulty valve or a clogged return line, the return line is for fuel flow back to that tank when using that tank, I believe when the tanks are switched, there is a plunger affair in a switching unit in the frame that when the fuel pressure builds up on the powered up tank, it applies fuel pressure to tha plunger and also to the other pumps check valve, hence blocking the fuel from flowing to the other tank lifting the diaphram taking fuel to the least resistance which should be the tank it is drawing from. Broken Wire
