gas returns to wrong tank
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Mountain Pass
Joined: Sep 2011
Posts: 114
Likes: 5
gas returns to wrong tank
Hello out there, I asked for help on the 80 up page and didn't get any help so here I am. After driving my 91 f150 on the front tank only for 5 years or so I recently decided to fix the rear pump. When I removed the tank, it was rusted up beyond repair, so I installed a OE quality Bosch pump, factory Ford sending unit , and new tank. I did, however, reuse the old add on external check valve. When I get it back together and running, when I am driving on the front tank,it pumps the gas into the rear tank. I dropped the tank and installed a NEW external check valve, but again, same problem. Run on front tank, pumps gas into rear tank. So I drop the tank again and install another Bosch pump. I also air check the external valve. It will hold at least 60# of air pressure from the line side (front) into the tank. Put it all back together and same problem, when you run on front tank it runs fine but pumps the gas into the rear tank. Running on rear tank and everything is fine. I need some help, thanks.
Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
Did you replace just the pump, or the whole fuel delivery module? There is a shuttle valve in the FDM inside each tank. To the best of my knowledge, the external check valve was a recall repair. If the external check valve works, the fuel is returning through the return line through a defective shuttle valve in the rear tank FDM.
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Mountain Pass
Joined: Sep 2011
Posts: 114
Likes: 5
yes
In response to your thread, I did replace the entire fuel pump module (a white plastic housing with the pump buried inside somewhere). I also replaced the hanger assembly due to rust issues and also the sending unit. As the original post indicated, I used Bosch OE quality parts from NAPA. If I am seeing 35# fuel pressure at idle with the regulator connected, wonder how fuel can be getting through the "recall" check valve when I couldn't blow 60# of air through it? I appreciate you taking the time to respond. thanks.
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Mountain Pass
Joined: Sep 2011
Posts: 114
Likes: 5
one more item
One more item that I noticed about the two fuel pump modules that I used is that the return line part of the hanger just empties into the module in a hollow cavity. If you look down in it you can see part of the electric motor inside and I can see no sign of any "shuttle" valve. Also, the volumne of fuel being put into the rear tank is substantial. I can drive 20 miles and in that length of time it will put what is left of 6 gallons in the rear tank. Thanks
Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
I haven't put my hands on one of the fuel delivery modules, but if the return line just empties into a cavity, I'm thinking that's a problem. What happens if you take out the external check valve - it is on the pressure line, right?
Thread Starter
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Mountain Pass
Joined: Sep 2011
Posts: 114
Likes: 5
I think I have decided that the fuel pump module for a truck with side and rear tanks must use a different rear pump than one with only a rear tank. The local NAPA cataloging really doesn't make much of a distinction about this, only the material the tank is made of and the gallon size (has anybody seen a plastic rear tank on a 91 F150?) At O'Reillys, there is a different listing. The pump it offers for my application has a markedly different look at the area where the return empties into it. I think all of my front tank return is ending up in my rear tank. I'll tell the rest of the story in a few days.
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