84 CJ7 Fuel Gauge Issue

The fuel gauge (which is brand new) will not read full when the sending unit is at 10 ohms (which should be full). The range of the sending unit is from 10 ohms full to 76.5 empty. I have shorted the sending unit lead to ground and the gauge goes to full, however, when connected to the sending unit (I have it out of the tank) it does not read properly, and max about 3/4 of a tank. I have checked that I have good grounds, which I do, and also checked for 12 volts at the I terminal of the fuel gauge (which I have). The only anomaly is that on the A terminal. Or jumper terminal to the temp gauge I have 12 volts also. Shorting the temp sender input to ground the temp gauge goes approximately half way. To be frank, I don't know what else to check. Thank you

 

The jumper/regulator strap runs from a voltage regulator inside the fuel gauge (terminal A) to the temperature gauge (terminal A). A voltage reading at terminal A of the temperature gauge should be about 5 volts. A 12V reading at the temp gauge terminal A means you have a bad regulator.
Possible that the vr is bad in the new fuel gauge
Welcome to the forum, hope you get it to work, and I always enjoy seeing forum members Jeeps so post some photo's of the CJ when you get a chance.

 

Thanks so much for your reply. If I have 12v at the temp sender A terminal, should I assume that the temp gauge is also now defective? Can I install the fuel gauge without the jumper attached to the temp gauge to check the fuel gauge and also for 5V at the A terminal of the fuel gauge without damaging the fuel gauge? Picture of the CJ, as you can see, a work in progress. Appreciate all of the help

 

Looking good. Raptor bed liner? That's what I put on mine and it's great. Don't have to worry about scratching the paint when driving overgrown trails. The printed circiut board for the stock YJ gauges was causing them to work intermittently so I changed all of mine to Autometer. Changed the tach to Autometer for the V8, added charger boost and fuel pressure gauges. Only factory gauge left is the speedo. Not quite as shiny, but still works great.
The CJ's voltage regulator for the gauges is built into the fuel gauge. Getting 12 volts at terminal A on the temp gauge means that the regulator inside the fuel gauge isn't working. The temp sender might still be OK. Morris 4x4 has all of the ohms readings for testing your gauges along with some great info on how the gauges work.
Here's the link: https://www.morris4x4center.com/knowledge-center/CJ-Gauge-Troubleshooting/
Best of luck. Looking forward to seeing future photos of the progress.

 

Thanks for the reply and information. Yes, I think the Rino Lining makes it scratch proof and I am hoping rust proof, as I live in Ohio, a rustbelt state!. I considered aftermarket gauges but really wanted to try to keep it as much stock as possible. If I can't get this issue resolved, as I have thrown a fair amount of money at it, I am considering the Dakota gauge package for it. Thanks for the link to the gauge troubleshooting article, it will help a bunch. I will upload photos as progress moves forward and thank you again for your reply. Take care and stay safe

 

Groundfault, I have looked at the information for checking out a fuel gauge, and I have performed this test, sadly, on 2 gauges and the readings do not match the troubleshooting guide. The first gauge I believe is faulty as the readings are not even close. The new gauge I checked today has a few similar readings but not within the specs of what is listed. I was wondering is the fact that the specs listed for troubleshooting are for a factory gauge with a factory jumper and not for an aftermarket gauge. Just wondering what your thoughts might be. I have not yet installed the new gauge but will do it this weekend. I did change out the sending unit, but I believe that the old one was ok, but the new one also reads right on the number with an ohm meter. Thanks again and stay safe

 

New fuel gauge may not have the same readings as oem. You might want to try fuel by itself first. Because of difference between the oem non-linear gauge, the aftermarket one may be right at full and empty, but the needle could be off for everything in between. Try it without the strap to temp and meter voltage out on strap terminal for 5v to make sure you're not going to send 12v to the temp gauge before it's reconnected.
If they're not playing nice together, my only suggestion would be to find a used oem fuel gauge.