After installing and testing (outside tank) my Equus fuel gauge and NEW sender, I reinstalled the tank and filled it with gas. The gauge now shows only 3/8 full with a full tank of fuel. The float inside of the tank must be stuck, since it worked OK outside the tank. Will some rough driving possibly work to get the float working again without dropping the tank again? I know just the trails that would make the fuel splash around in the tank quite a bit.
some claim if you tap the gas tank with a hammer, it will loosen the sender, but then again, in the FSJ manual it says to check the tank for deformation. I measured my stock 15 gallon tank and had a reading of 10 inches from the lip. I was told a 6-12 inch adjustable GM sending unit would work. Another thing I would question is this, is the sending unit matched in ohms to the fuel gage. There are some gauge specific out in the aftermarket , match the gauge up to the sender either 240-33 to 240-33 or 0-90 0-90. Im thinking maybe the sending unit isnt matched to the gauge, or you need to adjust the sending unit again by a hair. I am planning on doing this as well, hope it works out great for you.
I have had this issue before. You should just drop the tank. Make sure the float is in the right position. I had mine turned the wrong way so it was getting pinned because when it tried to rise up it was hitting the side of the tank. If the pickup and return line tubes are pointing to the drivers side it will hit the side and be inaccurate.