Tank Sending Unit Bad? - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 05-30-2019, 10:28 AM Thread Starter
 
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Tank Sending Unit Bad?

Working on a 1968 GTO Convertible with 400/ 4-speed. The last time I filled the tank the fuel gauge needle went all the way over to Full...and stayed there. Drove the car a bunch of times and the needle is still MIA so I searched the threads here and there was a good procedure posted to help identify the problem. I just want to be sure I'm drawing the right conclusion. First, I checked the ground to the sending unit by removing the connection to the trunk pan brace, cleaning it up and reinstalling it. No change. Then I disconnected the tan wire in the trunk and turned the ignition on. No change. With the ignition on, I then grounded the tan wire and the gauge swung all the way over to Empty. When I removed the ground, it swung all the way over past Full. Then I checked the resistance of the sending unit by putting a VOM between the tan wire leading to the sending unit and ground, and I got.....infinity. That implies that there is an open somewhere.

So, my conclusion is that the gauge is good but the sending unit has gone bad and I have to drop the tank and replace it. I'm just looking for some validation here because for someone without access to a lift dropping the tank is a pain. Any thoughts are welcome. Thanks!
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post #2 of 6 (permalink) Old 05-30-2019, 09:57 PM
 
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Sometimes the swing arm on the sending unit gets real rusty and will hang in the wide open position without returning. New sending is pretty easy to replace, just drop the tank.

If the gauge were bad it would stay on empty and not full so your suspicions are most likely accurate.

2006 GTO M6

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post #3 of 6 (permalink) Old 05-31-2019, 04:47 PM
 
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Yeah I think you are right, bad sender, GTO44 is spot on as well. Just a note for thought when you have to drop the tank and replace the sending unit.

The fix for running cool fuel is a return line to the tank which requires a sender with a return line. As easy as replacing one with a single line. If you are running a return line you might want to consider putting in a sender with a return line and even a return fuel line,..even if you leave it dry and plugged up for now. If you ever get into vapor lock or hot fuel problems hooking up the return is a simple matter.

I recommend them for all cars of this era, as the fuel that keeps moving stays coolest.The hardest part with no lift is wrestling the tank out changingbthe sender and adding another return fuel line.

If you have it already disregard if you donít your repair can upgrade the car for the same work, and you donít have to do it all now.
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post #4 of 6 (permalink) Old 05-31-2019, 05:14 PM
 
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Sorry I meant if you are NOT running a return line....you could consider it.

If your main fuel line is original, In-line tube can sell you an exact set of main and return and the sender. You want to replace those lines with the tank out which you will be doing anyway,...it is much easier that way routing the lines. It can be tough anyway, but you really need the tank dropped.

So you then drop the tank, install new lines, clean out the tank, and put in sender with return line. You can plug the return for now and later make your easy plan to hook it up...

Just trying to save you a bit of work if appropriate!
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post #5 of 6 (permalink) Old 06-05-2019, 05:48 PM Thread Starter
 
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Thanks for the input

I'm going to drop the tank and replace the sending unit. I replaced the tank about ten years ago and probably should have done it then, but everything was working okay and I assumed that, like me it would last forever. Bad move! It DOES have the return line so I'm good to go there.
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post #6 of 6 (permalink) Old 06-08-2019, 05:57 AM
 
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If you have or know someone who has a motorcycle jack they work great for supporting the tank during removal.
It's like a floor jack with two arms.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Exhaust, Suspension, Alignment, Fuel Tank and Brakes.

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