Inconsistent gas gauge readings

[Glennster1]

I'm getting crazy readings on the old gas gauge, for a while the needle would just sit at empty.
The old girl sat for over a year, then last week I took her out and it was the same old story with the gauge, I put 5 gallons in her and the needle sat on empty.
Then this weekend I got her out again, decided to put another 5 gallons in and BAM.......The needle went to full.......I only drove about 10 miles after that and now the needle is on 3/4.........What the heck?!?!?!
I saw an old video that Cuda Cody did back in 2017, he talked about the ''Electro Mechanical Gauge Voltage Limiter"
Could that be the problem?
The temp and battery gauges ''seem'' to be working OK.
I appreciate any suggestions....THANKS!!!

[Bullitt-]

  Welcome to the forum 

The "battery" aka Amp gauge is sperate from the others so the voltage limiter is not in play.
IF the temperature gauge is working properly that indicates the voltage limiter is good.
Wild changes in the fuel gauge readings may be from a poor connection between the sending unit and gauge, a poor ground to the sending unit, which seems to be pretty common, and of course a problem with the sending unit.   Lots of folks report the new sending units to be inaccurate. Of course you may have a combination of issues.
  Easiest thing to do first would be to provide an extra ground to the sending unit and see what the results are.   

[Glennster1]

12 volt stuff, poor grounding is so often the problem. It been many years since I had the gas tank down, looks like it's time again.
Thanks for the input ! ! !

[Jay Bee]

I've had more issues with fuel sending units that you can count. Another common problem is the grounding point on the units themselves. There's a mod out there to add a wire from the arm to the case, I do that now on all senders. This video shows how erratic that ground could be and how stable it is once a wire is added. I used an A body sender for the demo. My "No.2" video shows it with the wire permanently soldered on.

[Jay Bee]

What the heck, here's the No.2 video.  This might or might not be your issue. Oh, and welcome to the forum too.

[jimynick]

Well! So you're not just a pretty face John?    Good info and good vids, too! Thx for sharing! 

[Glennster1]

Great info.....THANKS ! ! !

[Aloha Randy]

I have the similar issue. full tank read near full, 15 minutes of driving, gauge read just above half. Half hour later down the road, reads empty. It does the same after 3 senders (2 foreign and 1 USA made), 2 gauges and a Tanks Meter Match unit installed. Even installed the new digital voltage regulator on the panel circuit board. Same issue. Checked Blue wire from tank to gauge, looks good. And several of my friends with e bodies have the same issue. And reading back through the forum, it looks like this is one of the more common issues, but still very elusive. I will look into finding a way to attach a ground to the sender tank base or do you have to wire it back into the sender itself and take it out from the tank? Just crazy stuff. You would think you might get some variation after using 3 different sourced senders.

[Glennster1]

Jay Bee,
  Sorry if this is a dumb question but it's been years since I pulled the tank down and changed the sending unit.
I see where you soldered the wire to the arm of the sending unit....but where / how does that wire get out of the gas tank, or is it soldered on the under side of the sending unit?
Again....THANK YOU for you help ! ! !

[Jay Bee]

Here's a couple pictures with the wire on e body senders, The first I took from the web and added the text, the second one is mine. I like to keep videos short and to the point (I have a low attention span) but in this case perhaps I should have pointed out the wire in No.2

[Glennster1]

Excellent......You da MAN!!!!

[Jay Bee]

Nah, just passing on some info I learned from another site. Hope this helps you two gentlemen out.

Found an older thread with this stuff.
https://forum.e-bodies.org/electrical-and-audio/11/fuel-send-unit-and-gauge-issue/20886/

My apologizes for not posting this info when I first heard of it. But, in my defense, I had to do it first to verify the modifications effectiveness.

[chargerdon]

I also added a ground wire from frame to the tank...as that little ground clamp on the fuel line gets rusted and doesnt make good contact.   I put in a new...cheapo sending unit, and my gas gauge reads a little past the full mark when tank is filled...   stays there for about 20 miles then goes down to near empty mark.   

When showing near empty it will only take about 12-13 gals to fill despite being a 19 gal tank.   This is consistent as if completely empty it will take about 5-6 gals to get it to move off of empty.    That's ok so long as i know...   d

[Glennster1]

GREAT work gentlemen!
I hope to get working on mine next week.
THANK YOU for putting in the time!!!

[dodj]

You don't need to drop the tank