So I just bought a 1988 E150 5.0 61,000 miles , dual tanks , this is what I know for sure , front tank is new , pump in that tank is new, front in line high pressure pump is new , fuel filter is new , dual tank switching valve appears new but dealer I bought it from said he did not replace it , he said maybe original owner . So as I’m driving home I find out that when I’m using the front tank it’s filling the rear tank and when using the rear tank it’s filling the front tank, everyone said the return line are switched, so I get under there and follow the lines from each tank and yes they were switched, so I switched them back , drive the van same thing happened, so I ordered a new switching valve and get a factory service manual, check fuel lines again , they are correct, so now I install the new switching valve and drive it , it’s still doing the same thing , not sure what to look at now, any advice will be greatly appreciated

 

There are shuttle valves in the in tank fuel pumps that are supposed to direct return fuel to the pumping tank. If these shuttle valves become ineffective, stick open, due to contamination with dirt,the pump assy in the overfilling tank needs to be replaced.
Most times guys don't remove the tank and clean it out when replacing pump assys. Because lines were switched , it probably sent junk from the other dirty tank into the replaced tank and,,,,,,,,,,,,,well you know the rest.

 

if i bypass the switching valve and just hook up the feed and return lines from the front/new tank to the front feed and return lines that feed the high pressure pump do you think that will work or will i need to replace the new pump in the new front tank , thanks

 

I have never tried it, but it sounds like it would work..

 

so, i decided to order a new rear tank and pump , I'm also going to replace the new pump in the front tank just incase it has been effected by some debris from the old/original rear tank , i was thinking about bypassing the valve but thats just not me, i want it fixed properly , thanks for the advice

 

Those older year Fords provided very good service when well maintained.
You probably won't have any further problems because you are doing it right.

Old tech's expression, "Do it right and do it once".

With your experience , you will be able to help a lot of folks that haven' been there yet, thanks.