OK. I have changed my fuel pump and now I do not have a working gas gauge. I did the tests and found out that it is a bad sending unit. But why is it bad? Why is it that you can pull the sending unit from the tank to replace the pump, put it back in and then have a bad sending unit. If the (+) side of the power is disconnected than there is no chance of there being a surge and the power will always have a return path. How do sending units work 100% one day and then all they want to do is wave at you when you are driving?

 

Broken grounding wire on sending unit, float stuck against the strainer, float arm bent and binding to name a few.

 

Tose are possibilities, but why does it wave at me. What I see is it will go from 1/2 tank to way past full and then to empty. "Waving." The Float would not be stuck, it could not move as fast as the needle does. A bad ground to the/on the sending unit is a possibility.

But the ground is braized on to the sending unit. How could there be a bad ground there. Also, If the fuel pump works I would think that it had to have a good ground.

 

Well since you have done the test and determined that the sending unit is bad, I guess that you have ruled out the fuel guage and the wiring.

 

Check on the wiring. I can apply Full, no, or partial ground to the gas gauge wire and get the correct gauge reading.

Maybe I have a magicall fuel tank and it just fills up while I am driving, kind of like mid-air re-fueling.