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Unread 11-13-2002, 10:10 PM   #1
Curly
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CJ7 gas gauge

I have a '84 CJ7 laredo with a gas gauge showing full all the time. Just started couple of days ago, the temp gauge seems to be going screwy too. After a little reading it appears that the two are connected in some way? I am guessing that this is a sending unit problem because when I dissconect the sending unit wire (pink) from the back of the gauge I drop to empty. Is there any way to be sure it is the sending unit before I go tearing out the gas tank to replace it? Thanks in advance for any help you can give.

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Unread 11-13-2002, 11:12 PM   #2
jeepdaddy2000
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A "full" reading indicates a ground between the gauge and the chassis. The first thing to check is the sending unit wire. Follow it from the gauge back to the tank and see if it is grounding to the frame. If you can't find anything wrong, then you will have to pull the wire from the sending unit. This usually involves droping the tank. Keep the tank grounded and unplug the wire. The gauge should now go to empty, indicating a faulty sending unit.
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Unread 11-13-2002, 11:21 PM   #3
Jeep Daddy
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This link should just about cover all your questions. It's quite accurate. I had to replace both - gauge and sending unit. Keep in mind, if you replace the gauge, you have to replace both gauges. The Temp gauge is tied into the fuel gauge electrically.

Gauge Info
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Unread 11-14-2002, 12:42 AM   #4
Curly
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thanks for the tips guys, I will give this a try tomorrow.
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Unread 11-14-2002, 05:27 PM   #5
Curly
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Okay here is the deal. I followed the pink from the tank and found that it had grounded itself to the tail light wire where my trailer lights attach. After correcting the problem I have no gauge at all so I am assuming that this has burned out the gauge? Bummer. Off to the parts store I go, thanks again for the help guys.
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Unread 11-14-2002, 10:27 PM   #6
jeepdaddy2000
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Not so fast, take another look at your repair. Be sure that the wire is good. While your there connect the test light to the bare wire.The light should blink and gauge needle should rise. If this happens, then the problem is between the repair and the sending unit. Look under the body and see if you can observe the wire going into the sending unit to be sure it is connected.
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Unread 11-14-2002, 11:17 PM   #7
Curly
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Okay now I am getting confused,,,lol. I connected my trusty test light to the bare pink and grounded it to the frame, sure as can be the light is blinking and the gauge rose to about a quater tank (which is wrong filled tank yesterday). What does this tell me? Maybe I have read too much about this? going back out to the garage to see what I can find from the bare wire back to the tank. You guys are great, really dont want to spend the $100.00 for a new cluster unless I have to.
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Unread 11-14-2002, 11:30 PM   #8
Curly
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well as i'm sure you already know there is no real way of getting a good look at the connection to the sending unit without dropping the tank. But if I follow you correctly the light test is telling me that something is probably bad with the sending unit and not the gauge?
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Unread 11-14-2002, 11:53 PM   #9
jeepdaddy2000
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Quote:
Originally posted by Curly
well as i'm sure you already know there is no real way of getting a good look at the connection to the sending unit without dropping the tank. But if I follow you correctly the light test is telling me that something is probably bad with the sending unit and not the gauge?
Yes, the light provides a resisted ground to the gauge, which is what the sending unit is. If the light blinks and the gauge goes up, then the problem should be past the light. Check the wire for breaks. I don't know if the fuel gauge has ever worked, but it is common for the float on the sending unit to "spring a leak" sinking to the bottom of the tank. This will give you a constant empty reading.
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Unread 11-15-2002, 12:05 AM   #10
Curly
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Just out of curiosity, is the "blinking light" a result of the regulator strap/points from the fuel gauge to the temp gauge and if so would this mean they are working right? Sorry dont mean to beat this thread to death just like to have the knowledge.
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Unread 11-15-2002, 12:13 AM   #11
jeepdaddy2000
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No problem, this is a forum, if you have a question, ask it. Anyway, the blinking light tells you the voltage regulator in the gas gague is working. The needle going up tells you the gauge works. The voltage regulator also runs the temp. gauge, which is what the jumper strap between the gauges is for.
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Unread 11-18-2002, 03:46 PM   #12
likestogofast
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I went a bought a sending unit when I had problems with my gauge and just hooked it up under the dash before I dropped the tank to make sure the gauge worked. Just move the sending unit float up and down to make sure the guage works. Chances are real good that it's the sending unit. I have replaced my '86 unit twice.
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Unread 11-23-2002, 05:51 PM   #13
Curly
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WooHoo!!!

Just a quick note to say thanks for all your help. I now have a working gas gage. Dropped the tank this morning and put in the new sending unit. All is well in my Jeeping world. Thanks again.

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Unread 11-23-2002, 09:08 PM   #14
Jeep Daddy
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How's the calibration? I bent my arm to read E when it was Empty, but the calibration isn't very good the rest of the way up the scale. 1/2 full means 1/4 tank. etc...
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Unread 11-23-2002, 09:35 PM   #15
Curly
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Good question!!! I didn't really think about that too much. I did take a close look at the old and new sending units and the bend in the arm seemed about the same although I do seem to have a lot of gas right now, lol. I figure I will just let the dam thing run out of gas and note the reading on the gas gauge.
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