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Problem with fuel tank switch over valve.

I got this truck a little over a year ago and we did a bed-off restoration. We dropped the fuel tanks and everything on the frame and painted the frame. We also put headers on the engine because the original manifold was cracked. In order to do this we had to delete all of the emissions. When we put it back together one of the inlets on the fuel tank selector valve broke off. We bought a new one and mounted it to the frame. After we started running it for a while and made sure everything in the motor was good we filled both tanks up completely. When we were driving it on the front tank down to the muffler shop to get the new exhaust installed gas started pouring out the gas cap of the rear tank. We stopped, took the cap off the rear tank, it was overfilled and extremely pressurized. We came to the conclusion that fuel was being sucked from the front tank to the back tank. After we got it back from the muffler shop, we got another selector valve thinking that the one we order was just a bad one. After about one week, the same thing happened again. So we know when we drive on the front tank gas goes from the front into the back and when we drive on the back tank gas goes from the back to front. We tried switching the return lines and it just transfers faster. This was one of the first years for EFI so everything is a little weird. A fuel line and a return line come out of both tanks and connect at the switchover valve. From the switchover valve one fuel line and one return line run to a high pressure pump and then to the engine. There are no electronics coming off the switchover valve. It runs off vaccum from the tanks. Also, coming out of both tanks is a breather line that connects behind the cab and then runs into the engine bay. The breather originally went to the emmisions stuff and now it is just an open line in the engine bay. We took it to two mechanics and watched several Youtube videos trying to fix the problem but it still occurs. Is there a simple fix for this problem or do I just have to deal with it.
 

d-kuzmen

Master Ford Tech
2,109
79
Connecticut
Back in the day Ford had us putting check valves on the fuel lines to prevent this. It was a recall.not sure if the parts are still available.
 
This is good to know about the check valves. Because id read thread after thread about the switch over valves doing exactly what the op talked about when they went and new ones having the same problems. But the fix was always replacing it again and problems going away. So nice to know about the check valves.
 

d-kuzmen

Master Ford Tech
2,109
79
Connecticut
We didn’t see anything like that on the lines. Where on the line does it go and does it prevent fuel from returning all together? I did not previously know about this, thanks for the information.
It goes. The line coming out of the fuel pump. Stops pressured fuel from entering the tank.
 

d-kuzmen

Master Ford Tech
2,109
79
Connecticut
Ok. Do you know a place where I can get high quality check valves? I don’t want to get one and it break a month after I buy it. If you were putting these on your truck is there a certain brand you would use? Thanks for all your help.
I would probably first check with my local dealer and see if they or any dealer still has the kit you can purchase. You will also want to replace the pressure regulator on the fuel rail as I think that was the main culprit.

C4A77CED-8E8D-4B65-8057-E0458915CE91.png
 

d-kuzmen

Master Ford Tech
2,109
79
Connecticut
There are 5 dealers in the us that show they still have in stock. Crappy pic but the phone numbers are there. You could give them a call see how much to ship to you.

528605C4-D707-4542-94B2-6C42273846A7.jpeg
 
Ok so I put the check valves in and it seemed to work but didn’t completely fix the problem. Then I put a new pressure regulator in and it stopped transferring the fuel back and forth for about a day or so and now it does it again. Is there anything else that I could do to fix it or is that it?
 

d-kuzmen

Master Ford Tech
2,109
79
Connecticut
Ok so I put the check valves in and it seemed to work but didn’t completely fix the problem. Then I put a new pressure regulator in and it stopped transferring the fuel back and forth for about a day or so and now it does it again. Is there anything else that I could do to fix it or is that it?
If you have a fuel pressure gauge I recommend testing the fuel pressure make sure the pressure isn’t to high. Usually that combination fixed the issue. I suppose it could be possible the new regulator failed.
 

dustybumpers

don't play well w others
They are not check valves, but are pressure regulators to keep from blowing out the check valves.
If you put those on a 87-89 you will have a real problem as that IS NOT THE PROBLEM.

the recalls were for 92-97 which has a check valve in the fuel pump. Those turcks have a 2 pump high pressure in tank pump. check valve in pump to keep fuel from retirning to wrong tank. RECALL IS NOT FOR YOUR TRUCK

87-89 has 3 fuel pumps. 2 low pressure in tank lift pumps, 1 in rail high pressure pump. NO CHECK VALVES

there is a fuel delivery module in the frame where all 4 lines, from both tanks go into, 2 lines come out of. this is your problem. the valve inside is stuck. these units are not rebuildable and need to be replaced.
 
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