I have an 89 F150 with the 4.9 L6 with dual tank set up. The front tank is brand new with a new sending unit and new pump. The low pressure pump in the front tank is not keeping up with the inline high pressure, what would be the first to check out? Fuel pressure goes erratic when switched from rear to front, symptoms are as if the fuel filter is dirty but it isn't (as it works just fine rear tank). Thanks.

 

Common in pre-90's.

See Link: http://www.stangler.com/motorsports/...alve/index.htm

 

So do I need to replace the valve? Clean it? Replace the diaphragm? The link is very helpful in assembly which would help in repair, but what is causing this problem? Thanks

 

For whatever reason, Diaphragm failure, o-ring becomes dislodged & interferes w/ the mechanical function of the valve (It is actuated/ change flow pattern by whichever in tank pump exerts pressure).

Personally, I'd go to a bone yard & grab one off a pre-90's dual tank E or F series truck.

 

Alright, I shall see if I can get my hands on one, thank you for the help.