ok, I am working on a 92 RS 305 tbi,
i been having issues with the speedo but got that straight and I an now zeroing in on the gas gauge.

I have been reading all sorts of problem with the gauges being stuck way over full, but that not my problem.
my gauge registers between 3/4 and just over full, of course when the tank is full it is reading fuel. but when it reads 3/4 it could be from 3/4 to E.

one strange thing is the gauge will float under breaking down to 3/4.

any ideas

 

You need to find out if the gauge or the sending unit in the tank is the problem. When you have the tank 1/2 emptied disconnect the weather pack connector above the rear axle and take a reading with the multimeter on the ohms side. I think our tanks are 0-90 ohm readings, if it is pretty close then the gauge is the problem.