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Discussion Starter · #1 ·
I recently had my gas tank out of my `70, and added a return line. After installation, the gage worked fine for about 30 miles, then it pegged to over full. Did I lose my ground? Or should I be looking at something else? Thanks for any help. Stan....
 

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I recently had my gas tank out of my `70, and added a return line. After installation, the gage worked fine for about 30 miles, then it pegged to over full. Did I lose my ground? Or should I be looking at something else? Thanks for any help. Stan....
Pull down the rear license plate, by the filler neck you should see a TAN wire. (do not confuse it with the BROWN wire that feeds the license plate lamp). There is a rubber connector boot. Pull this apart. In the half that leads back into the trunk, stick in piece of bare copper wire in it. Turn the ignition to "ON", touch this wire to a clean ground, the needle on the gas guage should drop like a stone to "E". Unground it and it should go way past "F". If it does, guage is good--most likely a ground issue.
 

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I may be wrong but I think full ground gives a full reading and open ground gives a empty. Usually you can unplug that sender wire in the trunk, see what happens. Gary
 

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I may be wrong but I think full ground gives a full reading and open ground gives a empty. Usually you can unplug that sender wire in the trunk, see what happens. Gary
Gary,

Actually an "open" or infinite resistance will result in the "way above full" on the gauge. The senders are 0-90 ohms. (the '64's are the only year w/ a 0-45 ohm sender). 0 ohms, or a short to ground on the sender wire makes the gauge fall to Empty, an open (much greater than 90 ohms resistance makes it swing past full). This is why most complaints start with "my gauge doesn't work, it shows way past full all the time" as most electrical issues are related to bad grounds.
 

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Discussion Starter · #6 ·
I checked the ground and it was tight with a clean contact, so as Joe suggested I opened the licence plate and was in the process of checking the brown wire, when I found it completely unplugged. Evidently when I pulled the tank I pulled it apart, I didn't realize it had a plug at that point when I pulled the tank, it must of come apart just barley hanging on, because it worked for about 30 miles before the over full gage concerned me. So now $60.00 later (worth of gas ) is says full, and is correct. So thanks for the suggestions, it led to a good end. Just a note, while I had my tank out I replaced the pickup tube screen, I ran into a guy at the Chev parts dept that really dug around for me, obviously their books don't go back to 1970, but he found a screen that fit my pickup, it`s 3/8" and the part # is 5651702, that's a GM#, Thanks, Stan.....
 

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I have a 65 El Camino where the full gauge goes from empty to full when I turn the key on. But it never moves otherwise. I have driven it and put in gas in it to realize something is amiss? Any ideas?
 

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I can only find a picture of a tank for a sedan. Is the sending unit also on the top for my 65 El Camino? Think I need to find if the tan wire is connected to the tank?

How can I tell if the sending unit is bad?
 

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ANY break in the wiring--between the gauge and the sending unit; or between the sending unit and ground--will put the fuel gauge past the "full" mark.

Doesn't "have" to be a ground problem--it does have to be an "open circuit"; or at least a highly resistive circuit problem.

If the wire from the gauge to the sending unit is grounded, the gauge goes to below "E".
 
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