I am replacing the fuel pump in my 86 IROC, 305 TPI. While doing that, I am replacing the sending unit as well. The car was always reading full since I have purchaed it. I just plugged the new sending unit in, without the new fuel pump installed or installing it in the tank, to test it. The gauge will not go past half tank when I manually raise the float to full. Am I missing something here?? I am thinking I should be able to manually test the new sending unit outside of the tank by moving the float up and down to make sure that my new sending unit works properly. Any ideas would be great!!!

No - your not missing anything. I just connected a sending unit to my testing station and manually adjusted the float from full to empty and watched the neelde climb and fall.

The shop manual says 90 Oms at full and 0 at empty. I got 7.3 VOLTs when full and .6 VOLTS when empty. ( My battery might be a little low ! )

If your highesyt reading is around 3 VOLTS than I would think that teh sending unit might be the problem. If your getting 7+ VOLTS when adjusted to full than check for a bad wire, a bad printed circuit on the cluster, or a bad gauge.

Also, if the sender is not the problem, the connection at the bulkhead behind the passenger seat area where the harness plugs in can be the problem sometimes too. It is exposed to dirt and grime and sometimes the connection is just loose there. Clean that up and make sure you are getting a good positive connection there as well.

Thanks for the replies, Guys. I did the ohm check, 90 at full then goes down to 0 on empty. So I know my new sending unit is working. I can now install the new sending unit/new fuel pump and get the car back together. Then, start looking why the fuel gauge is not working properly.