I just recently traded my 96 gasser for my 96 PSD. Have spent a lot of money making it into what I want it to be, but started noticing some weird little quirks trying to determine the origin of and how to solve them. My gasser would show beyond the f on full on the gauge when you filled it up and stay there for a while and as it went down it would get empty and go beyond E on empty before the tank ran dry and you had to switch tanks. Now my PSD SHows above F when full doesnt stay there very long ann when it hits E I went to switch over so as not to run dry w/ a mech FP. I go to fill it up and only takes 10 gal. so It reads kinda weird right? Now recently its reading different fluxuates accordingly for the fuel volume added but runs dry at the top of the E when it feels like does the same thing on both tanks, so Im curious and not extactly where to start at,.. the floats or the gauge cluster,.....? Any ideas?

 

Well, all I can is is my experience with ford fuel gauges is similar to yours. My old '88 gasser would read full most of the time, then plunge to empty all of a sudden.
The gaugs on my '97 PSD do a better job of indicating how much is in the tanks, but I track the miles per tank with the odometer to be sure.
I just think ford fuel gauges are pretty innaccurate, is all. I never wanted to go to the bother of dropping tanks to get to the sending units when I could just see how many miles I've gone.

 

Mine does the same thing, you may want to check the wiring at both tanks as well as the valve for switching tanks. There is a post on here about loose or corroded wiring connections causing this.I just keep track of miles on odometer and ignore the fuel gauge.