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Fuel Gauge Issues

Discussion in 'Early CJ5 and CJ6 Tech' started by JMNardo, Aug 27, 2006.

  1. Aug 27, 2006
    JMNardo

    JMNardo New Member

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    I have been trying to figure out what's wrong with the fuel gauge on my 59 CJ5. It typically reads 1/2 full when its empty, and pegs the needle when its full. If I remove the sending unit from the tank and let it hang free, it reads 1/2 tank so its not float adjustment. I have replaced the sending unit, the ground wire, and the wire to the gauge. Nothing changes. By process of elimination, I plan on replacing the gauge next, but thought I'd see if anyone had any advise before I do. Thanks.
     
  2. Aug 27, 2006
    sparky

    sparky done Staff Member Founder

    Toowoomba, QLD
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    Check the Ohms that the float is putting out?
     
  3. Aug 27, 2006
    Rampdog

    Rampdog knuckle buster

    Sandy, Oregon
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    :?
    By letting it hang free shouldn't it be reading empty?
     
  4. Aug 28, 2006
    JMNardo

    JMNardo New Member

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    Yep, if was hanging free, you'd think it would show empty but it doesn't. I did check the resistance of the sending unit. As I recall, it was about 800 ohns when in the "up" or full position, and maybe 700 ohms when in the "down" or empty position. Thinking that wasn't much of a spread, I checked the old sending unit. It tested pretty much the same. Could be I need a more sensitive ohm meter.
     
  5. Aug 28, 2006
    brandon11130

    brandon11130 Master ghetto fabricator

    bethlehem PA
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    well i got a pretty good feul gauge, its called a home depot paint stick and a jerry can, i have never been left stranded! sorry no real answers
     
  6. Aug 28, 2006
    Rampdog

    Rampdog knuckle buster

    Sandy, Oregon
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    Reading through some older posts on this site, you should have from 10 to 73 ohms on the sending unit. Do a search here, this has been discussed before with some darn good information. That is why I keep on coming back! :)
     
  7. Aug 28, 2006
    $ sink

    $ sink Gazillians of posts

    Virginia Bch
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    does your gauge return to empty when you cut the power to it?
     
  8. Aug 28, 2006
    JZ

    JZ Member

    Huntsville...
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    Was the '59 a 12V or 6V orig? Seem to recall that the sender was the same, but there was a swap behind the gauges...
     
  9. Aug 29, 2006
    JMNardo

    JMNardo New Member

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    The system is 12 volts. There is an unused lug on the back of the fuel guage. Wonder if that is for 6 volt systems? (I tried it, the gauge didn't work at all)

    The gauge does return to empty when I turn the power off.
     
  10. Aug 29, 2006
    admin

    admin Administrator Staff Member

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    12V, there was no 6V that late in production.
     
  11. Aug 29, 2006
    Mark Mann

    Mark Mann Kermit

    Huntsville, AL
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    I imagine the gauge is the place to look. If your old sending unit is reading about the same as the new one I would say you can rule that out with a pretty safe margin.

    As for 12 or 6 volts- I see it has been identified that a 6V system was not available this late. I can only assume that this is correct but is should make little difference as for how the fuel gauge works. In theory the sending unit is simply a linear device that proportions the voltage to the gauge and thus resulting in full/empty reading (or somewhere in between). This is basically what allows me to draw the conclusion of the gauge. Please give some feed-back as this is just an off-the-cuff answer based on what I have read here.

    -Mark :flag:
     
  12. Aug 30, 2006
    JMNardo

    JMNardo New Member

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    As suggested, I did a search and there is some very good information in this forum on the subject. One of the best linked to an article on the CJ5 instrument cluster gas and temp gauges. While the cluster in the article looks just like mine (1959), the article was written for the cluster on the later 1970's AMC CJs. Does anyone know if the gauges are interchangable with the earlier 12v Willys CJs?

    Mark; I came to the same basic conclusion. I know that the sending unit is really just a variable resistor, but I'm a little stumped since the gauge actually works, it just doesn't work right. I'm begining to believe my issue may be a poor ground at the gauge. I assume the whole instrument cluster is grounded through its mount to the dash so I'm not sure how to check this theory. I am also wondering about the voltage regulator built into the gauge. Its suppose to drop the voltage to 5 volts so if its not working the gauge is getting all 12. But I don't know if that make it read high.

    I hate electrical stuff.
     
  13. Aug 30, 2006
    sparky

    sparky done Staff Member Founder

    Toowoomba, QLD
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    If the gauge is getting all 12V it's shot.

    I think the fuel gauge will fit. It'll work too. The sending unit/voltage doesn't matter. The bimetallic strip just reacts to the heat/Ohms. So it'll function properly if you swap in a later one.

     
  14. Aug 30, 2006
    $ sink

    $ sink Gazillians of posts

    Virginia Bch
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    If the gauge returns to zero when the power is cut, the mechanism is probably not adjusted corectly for the sending unit's range of resistance. there are 2 small slots in the back of the fuel gauge. one adjusts the internal voltage regulator (adjust for an average reading of 5VDC) the other adjusts the gauge mechanism. you may want to try adjusting it before replacing it. yes all of the fuel gauges through the late 70's are interchangable. some look different, some work in the opposite direction, but if they came out of a 12v jeep cluster (3 terminals on the back) they will work in another cluster.

    HTH
     

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