NEW Gas Tank Sending Unit not working

[Canadian1968]

Alright you have done a lot . You really have narrowed it down.  You are getting 40 ohms off the peg of the sending unit correct ? This should give a reading 1/4 tank on your factory gauge (give or take ). The fact that gauge is barely moving tells me your gauge is getting a lot more resistance . Possible sources are your signal wire from the tank up to the back of your dash cluster . From there is goes threw a pin on your dash circuit board and routed to your gauge . You have already told us other gauges are working fine BUT that does not mean the circuit for gas is not damaged some how.  You said if your ground the sending wire back at the gas tank that it moves the needle ?  Did you actually let it get to full? Or did you jist see that it moves and pull it off. 

I would try this quick test again. And look for 2 things . Does the needle seem to hang up or stall anywhere threw the.sweep and does it go all the way to full . But do becarful once you see its to full remove the group  you can burn oUT the gauge if left on to long.

If it does not go all the way to full you can looking for the unwanted resistance in the circuit .  If it hangs up you may have to disassemble and see if your can repair the gauge .

[oldchevelle541]

Good information, when I grounded the lead wire the gauge needle responded by going towards full. I let it go 3/4 way so I would not create any damage. It did not jump, hesitate or other. Seemed to be a smooth steady motion. My factory gauge is en-route to Ohio for a rebuild. Will hook that up as soon as I get it back. If gauge responds I will get it transferred to the tank and we are back in business. If it does not will keep as a spare for the 70 Roadrunner which still has it's original sender.   

[oldchevelle541]

Folks,
just received my original sending unit back from John Wolf and Company in Ohio. $165 refurbished. A lot of money but if it fixes my long standing problem then all worth it.

Mark who works there is great. Bench testing it this evening Ohm reading goes from 11.8 to 78.8 so that looked good. I hook it up to the car without actually installing it and yes gauge now works.    But when I set the float to the full limit tab the gauge reads 3/4 tank. When I set float to half way point by eyeball gauge reads "E"  empty. Can someone tell me if this sounds legit or will it behave differently when in the tank. It is original gauge to the car but I had not owned the car when gauge was working hence cant say at the time it was accurate. Did not want to bend float rod  because the solder at the connection to the main shaft looks fragile.

[Canadian1968]

Your gauge needs to be recalibrated then .

If you put the unit to full, which as you said should be 11.8 ohms your gauge should be very close to full mark . Doesn't matter if it's in the tank or not

[oldchevelle541]

Thanks, after a long journey I put the original unit back into the car. Tank was near empty and I filled it up half way afterwards. Gauge reads 3/8 tank. That's good enough for me now since if gauge ever went to E I know I have a few gallons in there. Not going to remove gauge. It's never been out of the car and even though for some reason it is not accurate it at least works and tells me I have gas in the tank.

[Nacho-RT74]

I have to admit, being not in person to check anything I can think off, I'm pretty lost on this.

( I don't think an untoched gauge will miss the calibration by itself... not by that much at least!!! )