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'68 fuel sending unit

danf_fl

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I measured resistance and it shows 80.
I know there is fuel in tank.

I am asking for confirmation that maybe the sending unit needs replacement.
Thanks!
 
Hi Dan, I am no expert on this, but I have dealt with fuel sending units. I know that resistance changes from full to empty, but I'm not sure what the typical range is.

What exactly makes you think the fuel sending unit is bad? Gauge reading "empty" when you know you have gas?

The first thing is to make SURE the little (4" long) thin wire ground strap is connected to the metal nipple of the fuel sending unit & the steel fuel line. This strap keeps a ground connection in the fuel line where you have a small piece of rubber hose from the factory. It's a good idea to sand both the ground strap & the spots where it connects down to shiny metal to make absolutely sure you have a good ground. You can put a little spray of battery protector over the connecting ends once finished to keep those connection areas rust-free. A smear of Vaseline would work too.

Then, one good/easy test is to disconnect the gas gauge wire from the fuel sending unit & connect a "jumper wire" to it (alligator clip or tiny bolt that fits into the "L" connector), run that jumper wire to a known, good, clean ground (neg of battery for example), turn the key to the "on" position. IF the wiring & the gauge are good, the gauge should go completely to "full", then disconnect your "jumper ground wire" and the gauge should go completely to "empty".

If all that checks out OK, then the problem is in the sending unit. If your gauge is working, but just not reading right, other people on this board know what your resistance should read empty/full/half-tank.
 
I know one thing for sure on this subject:
Finding a good aftermarket sending unit for these things is damn near impossible.
All the Chinese ones suck.
They blow dead bear.
I'm saying they're no good.
Good luck finding an NOS one and if you do, prepare to pay through the nose.
 
if it has a plastic float and there is ethanol in your fuel , the gas slowly eats away at it and sinks or is half sunk. and throws the gauge off
it also attacks the floats in carbs, the new float we get for british carbs. are a solid black mass resistance to ethanol.
 
The fuel gauge shows empty.
I checked the unit from the post to gas tank, then again from post to another ground (this case, the muffler.)
Both times, I had 80 on the meter.
I understand that the range is normally 0-76
 
The fuel gauge shows empty.
I checked the unit from the post to gas tank, then again from post to another ground (this case, the muffler.)
Both times, I had 80 on the meter.
I understand that the range is normally 0-76
remember the tank sending unit is grounded through the metal clip from sending unit to fuel line
the tank is isolated with rubber so it sonnet ground is that strip
 
and easy test is wire disconnected the gauge should go to one side (empty our full) and if you ground it completely it should go to the other
so you will know where the problem is
 
The fuel gauge shows empty.
I checked the unit from the post to gas tank, then again from post to another ground (this case, the muffler.)
Both times, I had 80 on the meter.
I understand that the range is normally 0-76
Sending unit seems electrically ok then. Resistance reads higher when tank is empty. You'll still get continuity through the tank because it's strapped to the frame with metal bands. If there's enough gas in your tank to raise the float, I would suspect the float arm is stuck or the float isn't 'floating' as others have said..but as Miller posted you must verify the gauge works also. Ground that sending unit wire and turn they key on, only long enough to see the needle peg full(which hopefully it does). That will rule out the gauge or the wiring..good luck let us know if you get it
 
Beanhead, you just reminded me of what I experienced long ago. I had a 64 Dodge van and the gas gauge wasn't working. I filled the tank and drive a hundred or so miles so I knew the level was below the sending unit. I took it out and it looked fine. I had seen on someone else's that the windings had broken from wear but mine were good. I hooked a ground to it and plugged the sender back into the harness and turned on the key. Someone watched the gauge while I worked the float arm up and down and the gauge worked just fine. Re-installed it and it worked a few minutes and then went gradually to empty. Took it out and retested okay again. I thought the gauge was going but, just for the heck of it, I unclipped the float which was either copper or brass if I remember. Then I took the float to a bucket of water and noted it had two tiny holes in it where it was soldered together. Re-soldered and re-dunked to check and good to go. Re-installed in gas tank and good as new!
 
UPDATE: We dropped the fuel tank and removed the sender unit.
The complete sender unit (I suspect is original from 1968) was nothing but rust.
There were a couple of pin holes in the tank, so I ordered a new one (came with new sender unit).

With new tank and sender unit, all works as it is suppose to.
 
Coolness! Thanks for the folluw-up
 
resized_20180827_083050_1005-jpg.jpg

And I wondered why the gauge read "Empty"
 
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