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Thread: Fuel gauge.

  1. #1
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    Fuel gauge.

    I can't figure out this fuel gauge. One time when you turn on the switch it will go right where it needs to be, next time it goes all the way to the right past full. Works about half the time and about half the time it doesn't

  2. #2
    Super Moderator bmorgil's Avatar
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    Mark, usually full scale is a bad ground. Try jumping the ground on the gauge.

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    Super Moderator LarrBeard's Avatar
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    Mark, didn't you have temperature gauge problems as well? I think you replaced the original temp gauge with a mechanical gauge - but I could be getting my Jeeps confused.

    If you are having gauge issues, I still suspect the instrument voltage regulator as the culprit. If the regulator quits regulating and just applies 12-volts to the gauges, the fuel gauge will go fullscale.

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    Yes, the temp gauge wouldn't move at all so I went with a mechanical gauge. I think it was just a bad gauge. I have checked everything I can think of on the fuel gauge to check. It worked yesterday when I filled the tank. I watched the gauge move up like it should. Later I went to move it and it went out of sight over full. If if comes down to it, how would I know what gauge to get to just have a separate gauge and forget about the one in the cluster? I might try taking the wire that jumps from the fuel gauge to the temp gauge off and see if the temp gauge is messing with the fuel gauge.

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    OK, another question. Is the current regulator in the gauge internally. The gauge guy sent me a troubleshooting manual and when I started testing it indicated problems with the current regulator. I'm wondering if changing out the gauge would fix that.

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    Super Moderator gmwillys's Avatar
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    Sounds like the ground is intermittently making contact. That would explain the part time issue. I'll have to look at the gage I pulled out of the wagon. It should be the same as yours. If I remember correctly mine wouldn't read water temp either, but would read fuel level.

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    I don't mind fixing stuff, but I hate it when you buy new and it doesn't work. That chaps my a*s*s.

  8. #8
    Super Moderator bmorgil's Avatar
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    I am thinking you are chasing a bad ground.

  9. #9
    Super Moderator LarrBeard's Avatar
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    Quote Originally Posted by okiemark View Post
    OK, another question. Is the current regulator in the gauge internally. The gauge guy sent me a troubleshooting manual and when I started testing it indicated problems with the current regulator. I'm wondering if changing out the gauge would fix that.
    Arrrghhh....

    Troubleshooting over the internet is a pain in the tasssk.

    Your CJ 5 is a 1957 if I trace things back properly. It would have been an early 12-volt vehicle so at least originally the regulator would have been an external regulator that looked like a little sardine can. It was an obvious add-on to the cluster. It had a wire connected back to the rest of the vehicle (switched 12-volts from the ignition switch), either a little short wire or a tab going over to the gauges (oil, fuel and temp) and a ground terminal that was also a mechanical mounting.

    I've been guessing "regulator" - BMorgil is guessing "ground" and I think we may both be right. (Don't tell our wives, it's not my month to have a day to be right.)

    Take a good look at the ground tab or screw or whatever that mounts the regulator sardine can to the cluster, and check the cluster ground to the frame. No ground, no regulation - just 12-volts out and a pinned gauge.

    This isn't as complicated as mounting a wheat or corn head on the combine - its just trying to do it remotely.

    Now, "Is the current regulator in the gauge internally?"

    Not on the early CJ5's as far as I can tell. The early ones had a "two terminal" fuel gauge; one terminal went back to the regulator and one went to the sender in the tank. Later ones up in the 60's some time went to a three terminal fuel gauge with an internal regulator; one terminal was the switched 12-volts which went to an internal regulator, one terminal went to the sender in the tank and the third terminal was 6-volts or so that drove the other gauges.

    Since your gauge works properly some of the time, you have the two terminal/three terminal thing figured out.

    Look for a rusty/corroded/loose ground, like the lights on the grain trucks...

  10. #10
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    Well, first of all I can eliminate rust. Everything is brand new. Body, wiring, gauges, everything. It has a 12 volt alternator with internal regulator. I have a ground cable that goes from engine to frame. I also have a ground that goes from the back of the speedometer cluster to the body. Everywhere I check I get a good ground. I will look to see if I can find that "sardine can" in the old dash. The diagram shows a "12 volt" wire directly from the battery to the back of the fuel gauge and that jumps over to the temp gauge. This thing does read about 14 volts when it is running, maybe that is an issue.

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