Would a pinched or damaged sending unit wire to the fuel tank cause the gauge to read 1/2 a tank OVER full or is this a ground problem? Would getting POR-15 on the welded end of the ground on the sending unit also be a possible cause?
<BLOCKQUOTE>quote:</font><HR>Originally posted by supersport396_2000: Isn't it the other way round John? More ground=more movement in the guage,so an open sending wire would leave it at zero.The more resistance=more gas?<HR></BLOCKQUOTE>
Well, don't believe I am backwards this time. Here you are saying the same thing but have 2 different answers.
"so an open sending wire would leave it at zero."
An open is a very high resistance, infinity ohms. A short is 0 ohms. Gage goes full at 90 and higher above that.
The more resistance=more gas?
I agree. Infinity is greater than 90.
The 65 -72 Chevelles have a 0-90 ohms sender in them. When the sender float is down (0 ohms) the tank is empty. Full is about 90 ohms (except on the 64, which you can't get a 3/8 sender). Open sender wire is infinity (>90 ohms). Needle will peg super full if either the sender wire or the sender ground is open.
A simple test can be done to determine where your problem is. Ground the hot lead going to your sending unit with the ignition switch on. If the guage goes to empty, sending unit is bad, guage is probably good. rb6667
I just had that problem with my '65. The pointer was stuck past "full" as far as it could go. The cause was that the sender wire had come loose from the rear wiring harness plug. I'm not saying that is the only possible cause. It's just what I experienced with my car.
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