Thanks for looking into this RonJ@HT. We took a closer look and actually cut the wires going into the sender so we had good access to the resistance measurement.
We are still not sure why we are not able to read the resistance from the sensor by itself while still in the tank. Nevertheless we are able to get the data acquisition to read the level of gas.
It seems as if there is a charging circuit that allows the circuit to work. I know there is nothing in there that would behave like that. We were seeing this with a tank pretty empty, once we added more gas into the tank, we got better readings.
Thanks for the help if you have other ideas I would love to hear them. It is my understanding that the fuel sender is just a regular potentiometer nothing else. Unless you get one of those fancy senders that measure the capacitance of the gas