I'm having problems with my 1996 F350, 460 with dual tanks. The rear tank pushes fuel into the front tank. After a fill up, I always run on the front tank first then switch to the rear tank. Once the rear tank is low, I switch back to the front tank which now has another 5 gallons or so added from the rear.

I just installed a fuel pressure gauge and have also noticed under full throttle, the front tank fuel pressure is only about 20 psi; however it's a normal 40 psi when using the rear tank.

So do I have a bad check valve in the from tank FDM? If so, is it best to replace the entire front FDM?

Thanks for any advice.

 

As I understand it, yes, the check valve in your front FDM is bad if you are filling the front tank while running on the rear. And if your fuel pressure is that much lower when running on the front I'd guess your front fuel pump is suspect as well. So I think it's time for a new front FDM.