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95 F250 EFI 460 problems

11K views 9 replies 7 participants last post by  250/460 
"popped and went back to running strong"
Any luck on this issue? Have you looked into the tank selector valve? I am working on a truck with similar symptoms... VERY similar symptoms. That might as well be a video I shot. Last night I took apart the tank selector valve for cleaning and testing. There is a diaphragm that "pops" up and down on a detent system, actuated by pressure from whichever in tank low pressure pump turns on. So fuel pushes the diaphragm, from one of two tanks in one of two directions and it moves valves for feed and return between the two tanks, and the detent locks it in one of two positions... except when it doesn't. In my case I found disintegrated o rings, tons of crud, sticky valves and more.

Here is the thing... after cleaning everything seemed to be working fine but when tested wasn't. Blowing air at 5-6 lbs through one inlet only opened the valve half way... into the other would not move it at all. It's supposed to only need 5-6 lbs of pressure to switch... mine needed much, much more. So a low pressure in tank pump might not switch the valves completely...

What happens when it is half way between both tanks? VERY high resistance to flow. Random leaking into the feed line from other tank. Returning to wrong tanks return line or both return lines. All kinds of fuel supply problems.

Also it's worth noting that even when mine WAS locked in for primary tank the same symptoms persisted. AUX tank position worked great if I locked it that direction manually. Oh and fuel pressure readings appeared normal at the fuel rail this whole time. So basically I manually popped and locked mine into place for the tank I plan to use until I get this replaced.

Hope that helps. At least gives you something else to investigate. Now while I wait for the RTV to dry I might go ground my intake manifold just in case. Good luck!
 
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