Hello CA, hope everyone is doing well, it's been a while since I've been on here.
So I have a problem with my fuel sender, should be a relatively easy fix. I have the stock Moeller sending unit. When I take it off the tank, holding the sender in my hand and push the swing arm up and down, the gauge reads properly, with a full range from empty to full. When I mount it into the tank, something goes wrong. At first it always read 100% full, then I re-mounted it. I actually found out that there is only one way to screw down the sending unit despite the holes being symmetrical, so I went back to original mounting position. Now it always reads about 1/5 full, which is most definitely not the case.
Other things to note: I messed with it in the first place because it never went down past 1/4 full when it was empty. Also, I am missing one of the plastic washer type things that goes between the bolt and washer and the sending unit.