Fuel Gauge Help - JeepForum.com
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post #1 of 10 Old 05-24-2018, 12:11 PM Thread Starter
Jeepdvm
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Fuel Gauge Help

I know this is an ongoing issue for cj’s, but I was looking for some help. My fuel gauge drops to zero when engine is off. When I start the Jeep, it slowly goes up over a minute or two, but stops at halfway. No matter how much gas is in the tank, it always says half full.

Does this sound like a gauge problem or fuel sending unit problem? Any easy way to tell?

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post #2 of 10 Old 05-24-2018, 01:00 PM
hp_lovecraft
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You need a cheap multi-meter. $5 at walmart.
Set to "ohms" then measure the contacts behind the fuel gauge.

Assuming all the grounds and connections are good, sounds like a bad sender? If you measure the sender, should be around "73" when empty, and "10" when full. Sometimes the float on the sender falls off and no longer moves.
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post #3 of 10 Old 05-24-2018, 04:03 PM
walkerhoundvm
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I'm guessing someone installed a new sending unit at some point in the past, and gave up when it wasn't working correctly. You probably will have to replace the sending unit, after dropping the tank.

Source: I installed a new tank and sending unit last fall, and gave up when the gauge wouldn't go past halfway. I'm waiting until I get the tub off for a restore to go back in and fiddle with it.
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post #4 of 10 Old 05-24-2018, 08:34 PM
John Strenk
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Quote:
Originally Posted by hp_lovecraft View Post
You need a cheap multi-meter. $5 at walmart.
Set to "ohms" then measure the contacts behind the fuel gauge.

Assuming all the grounds and connections are good, sounds like a bad sender? If you measure the sender, should be around "73" when empty, and "10" when full. Sometimes the float on the sender falls off and no longer moves.
Disconnect the sending unit wire from the back of the gauge first or you will get a wrong reading.

Really a volt/ohm meter will quickly diagnose your problem.


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post #5 of 10 Old 05-25-2018, 10:38 AM
hp_lovecraft
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Quote:
Originally Posted by walkerhoundvm View Post
Source: I installed a new tank and sending unit last fall, and gave up when the gauge wouldn't go past halfway. I'm waiting until I get the tub off for a restore to go back in and fiddle with it.
I've gone through a few different senders over the years, and pretty much all of done that. I called one of them to complain (Spectra) and was told "all senders need to be calibrated to your setup".

Which is weird, since the 15-gal and 20-gal tanks use different senders. But whatever. People typically don't realize they need to "calibrate" until after the fuel tank is all back in. I didn't.

Dropping the tank is no fun. My current jeep has had to drop the tank 4 times in the last 12 years. 1st to fix a leaky tank, 2nd to replace sender, 3rd because I kinked the fuel line, then 4th, to replace the tank and sender. Dropping the gas tank is one of those things everyone should get to do once. Great fun.
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post #6 of 10 Old 05-25-2018, 10:50 AM
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I just put a new sending unit and gauge in mine, and it just goes to halfway. But, after re-examining how I put the unit in, I think I put it in so that the float is hitting the side wall. I thought I was paying attention when I installed it, but apparently not.

Probably not your issue, but it's possible.

I'm keeping this one until I die, or it kills me.
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post #7 of 10 Old 05-25-2018, 02:14 PM
walkerhoundvm
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Quote:
Originally Posted by hp_lovecraft View Post
words and stuff
I think I may have either put it in so the float is hitting the wall, or the sending unit grounded and went bad or something.

Before installing I did two things - checked with an ohmeter at float up and float down - completely within specs. I also attached it to the gauge and float up was full, float down was empty.

Has to either be hitting the sidewall or grounded out...
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post #8 of 10 Old 05-26-2018, 02:00 PM Thread Starter
Jeepdvm
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I might be heading towards dropping the tank. When I first got the Jeep, I ran out of gas because previous owner said gauge worked. It never drops below half way except when I turn the engine off.
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post #9 of 10 Old 05-26-2018, 09:01 PM
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Quote:
Originally Posted by Jeepdvm View Post
When I first got the Jeep, I ran out of gas because previous owner said gauge worked.
Years ago, I ran out of gas so many times I broke down at installed a Rotopax gas can. One particular time, I walked a mile to a 7/11, only to find they had no gas cans for sale. So, I filled an empty soda bottle I found in the trash. Just enough to get the jeep running.

So many things wrong with what I did. Love that Rotopax, though lets hope I'm never in any sort of crash.
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post #10 of 10 Old 05-26-2018, 11:17 PM
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I replaced the gas tank on my CJ-5 and at the same time, replaced the Spectra sendng unit I installed a couple years ago with a Crown unit. The readings are a lot closer now with the Crown than with the Spectra unit. Unless Spectra made changes to their resistive element, midscale resistance on their unit will not produce an accurate midscale fuel indication.
https://www.jeepforum.com/forum/f8/ga...-unit-4255297/
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