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1990 F150 fuel cross flow


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My 1990 F150 w/ 302 and dual fuel tanks recently developed a fuel leak at the front tank when the truck is running off of the rear tank.

I've done a bit of research and determined it's a known issue with the 1990-1993 trucks because of a check valve gone bad which causes the return fuel to be pumped into the front tank and then it starts overflowing.

Can anyone elaborate on what exactly the problem is and what needs to be replaced? I called my local ford dealership and they  Appvn told me their recall info only goes back about 10 years so they have no information on the problem.  SHAREit

Edited by SeanKarson
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I can't remember if that has a fuel tank selector on the frame rail or not. IF it has a block with 6 lines on it on the frame rail, it has a selector and the selector has failed. Pretty simple. 

 

IF it doesn't have a selector valve, you need to diagnose the problem. The pumps have a check valve built into the pressure side and a valve that opens on the return when the pump runs. Either could have failed, in either tank, OR the regulator.

 

You must check fuel pressure at the rail. Should be 35-40, key on, engine off.

-IF it is above 40-45 PSI, the regulator has failed and may be the whole issue. Replace the regulator and recheck. 

-IF it falls off, make sure there isn't fuel in the vacuum line to the regulator. IF there is fuel in the line, the regulator still needs replaced and you will have to start over.

-IF there isn't fuel in the vacuum line and it falls off, install the check valves in the recall parts list and start over. 

-IF the fuel pressure If it is normal and retains stable pressure for a minute, the issue lies in the return side. You will need to plumb a fuel pressure gage into the return line and see what it reads. If it is high (above 10 psi, IIRC), the REAR pump's return valve has failed. IF it is lower than that, the FRONT pump's return valve has failed. There is the possibility that both pump's return valves have failed, so you will need to recheck return line pressure once you replace the failed single pump.  

                                                                                                  

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38 minutes ago, SeanKarson said:

My 1990 F150 w/ 302 and dual fuel tanks recently developed a fuel leak at the front tank when the truck is running off of the rear tank.

I've done a bit of research and determined it's a known issue with the 1990-1993 trucks because of a check valve gone bad which causes the return fuel to be pumped into the front tank and then it starts overflowing.

Can anyone elaborate on what exactly the problem is and what needs to be replaced? I called my local ford dealership and they told me their recall info only goes back about 10 years so they have no information on the problem.

I forgot to tag you. There you go, see above

Edited by YT90SC
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