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post #1 of (permalink) Old 06-07-2005, 07:56 AM Thread Starter
 
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For real nitpickers....

For those who need to have everything perfect. One final adjustment....

Copied from a post on JU.

First lets have a look at the back of a typical OEM style Fuel gauge.


You probably never noticed the extra slots in the back but those are used for doing a calibration. They are actually quite clever in coming up with such a simple adjustment.

If you look inside an OEM gauge you will see two windings around two swperate bi-metalic strips. One is the often miss-labeled "Voltage Regulator" side and the other is for the needle or indicator movement.

As the windings heat up around the bi-metalis strip, one end of the strip will move. This free end is attached to the needle. The way the calibration works is there is a slot in the end of the needle were the pin on the end of the bi-metalicstrip fits. Depending upon the position of this pin in the slot determines how much the needle moves in relationship to the movement of BM strip. The closer the pin is to the pivot of the needle the greater the travel of the needle. THis is the Full Scale Adjustment. So if your gauge is not reading "Full" when the resitance is 10 ohms then you need to adjust the position of the pin.


THe other adjustment just sets the starting position of the needle or "Zero Adjustment" So if your gauge isn't reading empty when it's at 78 Ohms then you need to change this adjustment.

Note these adjustment are interrelated meaning that if you adjust the "Zero Point", then the needle might not reach "Full" so you will have to go back and re-adjust the "Full Scale" adjustment.

Start with the Zero Point first.

I attached the proper resistance (73 ohms) to the "S" terminal and ground and attached the power and ground leads.

I used 10-32 nuts and wire lugs to make the connection easier.
THen I adjusted the Zero point to read "E" as best I could using a flat bladed screwdriver. Then you replace the 73 ohm resistor with a 10 ohm resistor and adjust the FUll Scale adjustment. Note it might take a minuet for the needle to Stop moving so you might want to read a chapeter in your FSM while your waiting. [img]/ubbthreads/images/graemlins/smile.gif[/img]. It also makes several jumps when going to "F". THis is normal.

Now the replacement gauges I have work a bit differently. Mine was quite bent inside and needed an adjustment. Maybe yours was knocked out of cal also.


The Zero and Full Scale adjustment are in one place. Put the screw driver in one slot and you can adjust the Zero Position. Turn the screw driver 90* and you can adjust the full scale movement. The pin and needle mechanism is the same as the OEM guages. The screw on the side is for adjusting the regulator. It has a funky screw so you don't accidentally mess up this adjustment. .



Irregardless of how the adjustments work internally, the procedure is still the same as above. If you can't get the gauge to work properly after all this then I would recomend you send them back and get another set. THere have been some "Quality issues" with the vendor.

For more information on Gauges and stuff, Go here:
http://users.adelphia.net/~john.stre...QuickFacts.htm
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post #2 of (permalink) Old 06-07-2005, 08:15 AM
 
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Re: For real nitpickers....

[img]/ubbthreads/images/graemlins/goodpost.gif[/img]
[img]/ubbthreads/images/graemlins/applause.gif[/img]
[img]/ubbthreads/images/graemlins/40BEER.gif[/img]


Egg-sell-ent - this is a keeper.

Now if I can just work up the ambition to pull the gage on the one CJ I have where it works at all...

Maybe I won't run outta gas at 1/4 tank any more.

[img]/ubbthreads/images/graemlins/blush.gif[/img]
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post #3 of (permalink) Old 06-07-2005, 08:37 AM
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Re: For real nitpickers....

They problem I had with teh OE guage is the damned cardboard they mount the posts into. I stripped the posts out of the card board on two different guages before ordering a Eqqus (sp?) brand that is mounted in a more sturdy and durable plastic casing. now if I can figure out how to keep the needle from bouncing all over the place when te Jeep bounces.. :P

But cool info none the less. thanks John.
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post #4 of (permalink) Old 06-07-2005, 08:54 AM Thread Starter
 
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Re: For real nitpickers....

Twisting those nuts to tight will also screw up the calibration. I had one were the post turned and prevented the regulator from operating sending full current thru all the gauges. Smoke city.
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post #5 of (permalink) Old 06-07-2005, 09:24 AM Thread Starter
 
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Re: For real nitpickers....

[ QUOTE ]
They problem I had with teh OE guage is the damned cardboard they mount the posts into. I stripped the posts out of the card board on two different guages before ordering a Eqqus (sp?) brand that is mounted in a more sturdy and durable plastic casing. now if I can figure out how to keep the needle from bouncing all over the place when te Jeep bounces.. :P

But cool info none the less. thanks John.

[/ QUOTE ]

Where did you order these from? Equus maybe ??
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post #6 of (permalink) Old 06-07-2005, 09:53 AM
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Re: For real nitpickers....

Most excelent post Garth....I mean John
post #7 of (permalink) Old 06-07-2005, 11:29 AM
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Re: For real nitpickers....

[ QUOTE ]

Where did you order these from? Equus maybe ??

[/ QUOTE ]

From 4wdh after talking to CJSixer about them. The needle bounces around when you get off full, but when it bottoms out and stays there, it's time to fillup. So I guess it works... I know when it's full, and I know when it's time to fill back up! [img]/ubbthreads/images/graemlins/laugh.gif[/img]
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post #8 of (permalink) Old 06-07-2005, 12:26 PM
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Re: For real nitpickers....

Great info! Thanks!
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post #9 of (permalink) Old 06-07-2005, 01:06 PM
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Re: For real nitpickers....

John, as usual.... [img]/ubbthreads/images/graemlins/goodpost.gif[/img]
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post #10 of (permalink) Old 06-07-2005, 01:15 PM
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Re: For real nitpickers....

Great Post! [img]/ubbthreads/images/graemlins/yourock.gif[/img] But since you brought it up, I dont have a FSM and need to get the gauge working again. The Hayne's diagram is less than adequate and mentions that there is a 3watt resistor in or near the gauges. The PO of my jeep doesn't have anything hooked up to anything back there.

So I see you have four leads hooked up... If I'm on the right track, 12v goes through the sender (resistor), then to the S terminal (if I can figure out which one that is), then simply to ground? Or is there another 12v connection to the gauge for a reference? [img]/ubbthreads/images/graemlins/confused.gif[/img]
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