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Unread 11-18-2013, 09:30 PM   #1
GlennLever
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How do I tell which gas tank sending unit I need

I have a 1984 CJ-7

The gas gauge has never worked.

The whole speedometer cluster was replaced.

I'm going to pull the tank to clean it up, replace the rear brake line, and install a trailer hitch.

Quadratec offers four gauges, which one do I order, or do I order both and return the one I do not need?

MTS Sending Unit
For 72-86 Jeep® CJ-5, CJ-6, CJ-7 & CJ-8 with 15 Gallon Fuel Tank
Quadratec Part No: 55107.07
Manufacturer Part No: CJSU-1
http://www.quadratec.com/products/55107_07.htm


This is a crown unit and would prefer not to order this one based on past preference of their parts
Rear Mounted Fuel Sending Unit
For 72-86 Jeep® CJ-5, CJ-6, CJ-7 & CJ-8 Scrambler with 15 Gallon Fuel Tank
Quadratec Part No: 55107.02
Manufacturer Part No: 5357373K
http://www.quadratec.com/products/55107_02.htm


This is a crown unit and would prefer not to order this one based on past preference of their parts
Fuel Sending Unit Kit
For 81-86 Jeep® CJ-5, CJ-7 & CJ-8 Scrambler with 20 Gallon Fuel Tank
Quadratec Part No: 55107.0010
Manufacturer Part No: 5362090K
http://www.quadratec.com/products/55107_0010.htm


This is a crown unit and would prefer not to order this one based on past preference of their parts
Fuel Sending Unit
For 82-86 Jeep® CJ-5, CJ-7 & CJ-8 with 20 Gallon Fuel Tank
Quadratec Part No: 55107.03
Manufacturer Part No: J5362090
http://www.quadratec.com/products/55107_03.htm


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Unread 11-18-2013, 09:45 PM   #2
jimdubose
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pull yours, see which one it looks like, and...........

have you considered rehabbing yours (if it needs it or is salvageable, or there may not be anything wrong with it other than a bad ground)?

before you spend money on a new one, it may be something as simple as a ground wire. there are plenty of threads already on here on the gas gauge and sending unit. john strenk has urls for great write-ups on repairing and troubleshooting. I would take a look at one of them, for instance this one:

http://home.roadrunner.com/~john.str...for_cj_gau.htm
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Unread 11-18-2013, 09:53 PM   #3
GlennLever
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Quote:
Originally Posted by jimdubose View Post
pull yours, see which one it looks like, and...........

have you considered rehabbing yours (if it needs it or is salvageable, or there may not be anything wrong with it other than a bad ground)?

before you spend money on a new one, it may be something as simple as a ground wire. there are plenty of threads already on here on the gas gauge and sending unit. john strenk has urls for great write-ups on repairing and troubleshooting. I would take a look at one of them, for instance this one:

http://home.roadrunner.com/~john.str...for_cj_gau.htm

All true, it would be nice to gave the part on hand when the tank comes out so the Jeep is not inoperable while I wait for a part to show up

The temp gauge works so I would think it is safe to assume the voltage regulator in the temp gauge is working.

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Unread 11-18-2013, 10:17 PM   #4
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You have a stock 15 gallon tank. I would try to get one that comes with a new pick up filter.
Momentarily grounding the pink wire on the left side of the tank will test the gauge. Do this very briefly as you or someone watches the gauge. If it moves, break the ground.
Make sure the sending unit is grounded (top left of forward tank crossmember) and run an ohm test to check if its working....open and its most likely bad.
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Unread 11-18-2013, 10:40 PM   #5
jimdubose
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agreed, I would test the continuity of the wires from the gauge to the sending unit and the ground wire from the sending unit, checking the resistance of the pink wire to ground will also tell you where your float level is. fill the tank to the brim first, see if you get around 10 ohms, then you know your float isn't resting on the bottom of the tank, full of gas, eliminating that issue
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Unread 11-19-2013, 01:40 AM   #6
BagusJeep
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The second one.

Whilst you have the tank out it is a god opportunity to replace the rubber hoses above it which tend to rot and also clean and paint the tank and skid.
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Unread 11-19-2013, 02:10 AM   #7
John Strenk
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Well there is no voltage regulator in the temp gauge.
I would test to see if the regulator is working though.

This is best done by using a test light and connect one side to ground and the probe to the metal bar connecting the fool gauge to the temp gauge.
If you don't like contorting under the dash, simple pull the wire off the temp sensor and touch the test lamp to the plug at the end of the temp wire.

the MTS looks like it has the connection pointing the wrong way. when I hooked up my lines, I put in a big service loop so it probably wouldn't matter if they pointed the wrong way. Mine looks like the last one. It's still working despite burning it up once.
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Unread 11-19-2013, 07:50 AM   #8
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With a 15 gallon tank that eliminates the last two. Since you don't want a Crown product that eliminates the second one. Easy peasy!
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Unread 11-19-2013, 07:54 AM   #9
GlennLever
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Quote:
Originally Posted by John Strenk View Post
Well there is no voltage regulator in the temp gauge.
I would test to see if the regulator is working though.

This is best done by using a test light and connect one side to ground and the probe to the metal bar connecting the fool gauge to the temp gauge.
If you don't like contorting under the dash, simple pull the wire off the temp sensor and touch the test lamp to the plug at the end of the temp wire.

the MTS looks like it has the connection pointing the wrong way. when I hooked up my lines, I put in a big service loop so it probably wouldn't matter if they pointed the wrong way. Mine looks like the last one. It's still working despite burning it up once.
It has been awhile since I read your articles, regulator is in the Fuel gauge, correct? and if no current was coming out of it the temp gauge would not work??????

So order the first one and put in a long loop which would be good if it has to come down again, any other suggestions on the process of dropping the tank?

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Unread 11-19-2013, 08:00 AM   #10
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Quote:
Originally Posted by BagusJeep View Post
The second one.

Whilst you have the tank out it is a god opportunity to replace the rubber hoses above it which tend to rot and also clean and paint the tank and skid.
Not sure I want to paint, as it takes away from the survivor status, deferentially clean, remove and paint any rust.
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My restoration thread here on the Jeep forum
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Unread 11-19-2013, 08:55 AM   #11
jimdubose
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be sure it is as close to empty as you can get it, gas 'weighs' around six lbs/gal, and if you're the syphoning type, tastes like gasoline
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Unread 11-19-2013, 08:58 AM   #12
John Strenk
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Right, no current no workey,

However failure of the regulator is usually results in lots and lots of current, not a loss of current.

This could burn up the temp gauge if the engine gets too hot.
Why only if it gets to hot? because when the engine is cold there is a lot of resistance keeping the regulator from heating up too much. even at normal operating temperatures there is some significant resistance.

If something goes wrong with the engine and then it gets hotter, the resistance drops lower and more and more current passes.
I think it also damages the sensor and/or the gauge. My temp gauge seemed to work but after I 'fixed' the regulator the gauge read lower than expected.

This happens more often in the fuel tank because when you fill the tank, the resistance drops very low allowing too much current through the gauge and sending unit. Most of use fill the tank more than we overheat the engine.

This usually happens if the ground to the gauge is lost.


I would not assume the regulator is working just because the temp gauge is indicating

Even the quickly grounding the "S" terminal to see if the needle moves will prove the regulator is working.
Only using a DVM or test light will prove the regulator is working and it's safe to hook up your new gauges and/or sending unit.

And dang, need to fix that picture but I can't access my old ftp site anymore to change it.
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Unread 11-19-2013, 09:12 AM   #13
jimdubose
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so, john, if you take a fuel gauge and hook up the red and pink wires to the respective posts, and ground its body say to the neg battery terminal, but don't have the regulator to the temp gauge attached between both, you will get a faulty reading? any at all? damage the gauge?
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Unread 11-19-2013, 09:35 AM   #14
GlennLever
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Quote:
Originally Posted by jimdubose View Post
be sure it is as close to empty as you can get it, gas 'weighs' around six lbs/gal, and if you're the syphoning type, tastes like gasoline
Unfortunately it is full as I keep it that way because the gauge does not work. The good thing is it is premium and will get siphoned out and put into my wife's car before we lower it.
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My restoration thread here on the Jeep forum
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Unread 11-19-2013, 09:45 AM   #15
John Strenk
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Quote:
Originally Posted by jimdubose View Post
so, john, if you take a fuel gauge and hook up the red and pink wires to the respective posts, and ground its body say to the neg battery terminal, but don't have the regulator to the temp gauge attached between both, you will get a faulty reading? any at all? damage the gauge?
Not sure what you mean? The temp gauge or the fuel gauge?
The fuel gauge will still work as good as it had before, the temp gauge would not work if one side is not hooked up. Nothing should burn up.

The bar between the gauges is not the regulator, the regulator is in the fuel gauge.
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