On our '91 Wrangler with plastic tank it was this: inside the gas tank(once you remove the sending unit) you will see a white plastic trough. This was originally heat welded to the bottom of the tank and the sending unit float rests inside it. Its purpose appears to be negating wave action when the tank is low and which would make the float bounce up and down. Problem is the tank flexed with age and the heat welds gave out. The white plastic trough had become a battering ram and was consistently interferring with and destroying the sending unit. I never found a glue that would hold it in place. Best solution is to know your max. milage on a tank, set the trip odometer at fill up, and that is your new guage.