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  • Temp Gauge/Fuel Gauge wiring

    Just finished Rebuilt engine install (same 258 I6) on my '81 CJ7. Reconnected all the wires that I could to their original locations, except the ones that connected to the air pump hose that ran over the valve cover. The pump and air tubes on the exhaust manifold were rusted toast. The engine and new carb on the original intake manifold work fine. I connected the solid green wire to the intake manifold heat sensor as it was before.

    The problem: The Temp gauge does not work. It never moves even though the engine comes up to operating temp just fine and runs fine. I understand that in 1981 the two gauges acted together. Is that right?? The fuel gauge looks like it is working. I have looked at wiring diagrams and tried connecting the "purple and white" wire from the firewall wiring to the sensor. That didn't cause the temp gauge to work either. This is the sensor on the intake manifold and it was working before the rebuild began. Is there a "trick" to wiring up the the temp and fuel gauge connections when you do not have the old air pump hoses and air filter hoses any more??
    The oil gauge and alternator gauge work fine.

    Thanks for your help!

    PS: The "Pavement Pounder" thing isn't true. This Jeep sees lots of rough back roads, hunting trails and 'secret' fishing holes. Winter, Spring, Summer and Fall. Don't know where that came from!!!
    Last edited by D&BCJ7; 12-27-2005, 01:01 PM.

  • #2
    On Pavement Pounding...

    Originally posted by D&BCJ7
    PS: The "Pavement Pounder" thing isn't true. This Jeep sees lots of rough back roads, hunting trails and 'secret' fishing holes. Winter, Spring, Summer and Fall. Don't know where that came from!!!
    D&B, you're a pavement pounder 'cause you spend more time in your Jeep than on this forum...

    Yes... the fuel and engine temp share power. There is a mechanical voltage regulator built into the fuel gauge. However, you may have broken a wire, or something with all that work going on. I'd make sure I had continuity to the sensor. Here, I got two links for you. One is a high dollar instrument cluster just for CJs that I thought all the guys might like to see so I just threw it in: http://www.dakotadigital.com/index.c...rod/prd210.htm

    This one is for us PO' Jeepers who have to fix all their stuff with duct tape and balin' wire: http://www.off-road.com/jeep/tech/electrical/gauges/
    Last edited by blackwater; 12-27-2005, 01:20 PM. Reason: to add CJ

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    • #3
      Or you could go get a cheapie temp gauge with it's own sensor. I had the exact down to same troubleshooting you did before I finally said enough is enough and got a gauge. It's been mounted under the dash panel for about 6 years with no problem at all.

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      • #4
        confession time...

        Originally posted by texascj
        Or you could go get a cheapie temp gauge with it's own sensor.
        Penguin finally showed me the error of my ways on the electric temp gauge. Although I fiddled with my factory gauge 'till I got it working properly I also run a mechanical. (I have MUCH confidence in the mechanical gauge and having both makes me feel better in the summer.)

        Ya'll check that Dakota stuff out. If you're into the digital gadget stuff they rock.

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        • #5
          The two are not dependant, they are not even used the same way.
          The purple/wtrl is the one for temp from the engine.
          The book says to first check to see if fuel gauge moves, you did this.
          Next they say to pull the cluster and test.
          Me I would do the wire at the sending unit first, easier to get at.
          Pull the wire form the sending unit(purple/wtrl) ground this down, if your gauge moves, replace your sender, if the gauge doesn't move, then you will need to get under the dash and ground the terminal where the wire comes in. This should make the pointer move, if it does not then your gauge is bad, if it does you have a break in the line.

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          • #6
            Originally posted by Penguin
            Me I would do the wire at the sending unit first, easier to get at.
            Pull the wire form the sending unit(purple/wtrl) ground this down, if your gauge moves, replace your sender, if the gauge doesn't move, then you will need to get under the dash and ground the terminal where the wire comes in. This should make the pointer move, if it does not then your gauge is bad, if it does you have a break in the line.
            It is advisable to watch (or have someone else watch) the gauge 'cause if you ground the purple/white wire for too long, there is the possibility of ruining the gauge.(not tryin' to step on toes here Peng' bud)
            I've been there myself. I went through 3 sending units 'till I got one that worked. If you have a multitester, you could put the sender in a vice,heat it up, and see what the multitester reads both cold and hot. This would tell you if the sensor is boogered.

            Just a thought,
            ragg
            Last edited by raggmann; 12-28-2005, 01:53 AM.

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            • #7
              ?

              Originally posted by Penguin
              The two are not dependant, they are not even used the same way.
              Penguin, I'm confused by this statement. Am I missing something? Did I get something wrong? I was attempting to address this part of D&B's question: "I understand that in 1981 the two gauges acted together."

              The constant voltage regulator (cvr) in the fuel gauge serves power to both the fuel and temperature gauges. I seem to remember that it is somewhere between 5-7volts. The reason I didn't mention grounding the sensor wire was covered by Ragg. You can ground the gas sending unit wire the same way but if you short the supply for too long for either gauge you're going to lose both gauges due to damage to the CVR. Much better to use a meter.

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              • #8
                The two temp sensors have nothing in common. The one with the green wire runs the manifold heater and the purple/wtrl goes to the gauge.
                The fuel and temp are tied togeather.
                Yes raggmann, you are right, you don't want to have that connected for to long. Don't leave it connected all the time.
                When I was trouble shooting mine I had no top or doors so I could get from the engine compartment to the gauge really quick. All you need to do is see if it moves.
                As for heating the sending unit there are easier ways.
                Run the motor, let it start to warm up. Do an ohm check on the sender and the resistance will decrease with heat.
                Cold 73
                Beginning of band 36
                End of band 13
                Hot 9

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                • #9
                  Found it!

                  I finally got some time to do an ohm test on the sender and then the wire. Got continuity in the wire but not much change in the sender. So, I took the path of least resistance and purchased a new sender. Hot dog! Now I have temperature!
                  Thanks for all the help for such a simple problem. Sometimes you just need new ideas to help you think it through. Response to this threat was really full of useful information that I can use on the next problem that is sure to come up.
                  Happy New Year!

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