Scored an OEM Fuel Gauge Gage - JeepForum.com
 
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post #1 of 11 Old 05-19-2020, 10:45 PM Thread Starter
Capt_Drake
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Scored an OEM Fuel Gauge Gage

Actually got the whole 85mph speedometer minus the odometer and lights.

Here's some pictures of the inside, the top cover came off while removing, which is a little concerning, but all the wires are connected.

The resistance ohm readings between I / A terminal and housing is 84, not 50, but my fingers are crossed.

John, Good Sir, recommendation on source power to calibrate?

Mahalo
Drake

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post #2 of 11 Old 05-20-2020, 01:42 AM
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The fuel gauge contains its own constant voltage regulator, which in turn powers the temp gauge. These two instruments need a constant voltage or they will read wrong most of the time (like the oil gauge, which is voltage sensitive).

They come as a pair, did you also get the temp gauge?

I am sure John will tell you that it is not therefore voltage sensitive, so a 12V battery or 14.5V from an alternator will give the same reading.

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post #3 of 11 Old 05-20-2020, 04:37 AM
John Strenk
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Yes, that is right, it's not voltage sensitive. you can go from 6 volts to 48 volts without effecting accuracy.

Sadly a 9 volt battery is not going to have enough current to operate it.

If you hook it up to your car battery, Make sure you have a good ground connection. You will burn up whats left if you don't.

How are you planning on testing it?
Using test resistors or the fuel level sensor in the jeep?
Doing it inside the jeep?

Some of the bigger power supplies for laptops should be able to give enough current.

Most of the steps I've posted are with the gauge still in the speedometer housing. I'll have to post some pictures of how to test the gauge alone.
A little more care is needed.

https://www.jeepforum.com/forum/f8/q...-test-4390781/


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post #4 of 11 Old 05-20-2020, 09:24 AM Thread Starter
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Thank you both, I did get the set and the speedometer housing and faceplate (?).

I'll be following the steps in Calibrate your Gauges... and Quick Gauge Tests..., resistors will be here Friday, although it might be more appropriate to tune it to the sender I have, although that's an aftermarket that's already in the tank and from what I've read may fail soon, so better to go with original parameters.

I've added dedicated return (ground) wires from the tank area and dash to the battery (also from the starter, lights, alternator) by way of some marine grounding bus bars. Marine electrical hardware is the way to go, you can get cool stuff like this bus bar and cover for the supply side.




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post #5 of 11 Old 05-25-2020, 08:06 PM Thread Starter
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Well that didn't work. At 10 ohms it was way pegged and couldn't get it back with the adjustment and at 73 ohms it was a quarter of a tank, so I think the 84 ohms that I measured to begin with with a sign that it was bad.


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post #6 of 11 Old 05-26-2020, 08:28 AM
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Did you get a flashing light on the "A" terminal and DID you have a good ground?


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post #7 of 11 Old 05-27-2020, 07:49 AM
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You can calibrate the gauge by bending the sending unit arms, which you do with the tank dropped and sending unit on the floor. They are not exact resistances. I set mine so empty is empty if I can and do not worry about full etc. Not so easy as recalibration means dropping the tank and i have other ways to spend my days.

Bagusjeep is now empty when empty, had to replace the sender which had been repaired at least once, full lasts a long time. Puthijeep was not a great success as it also needed a new sender but now says full when full and empty is about half full (with a 20 gallon tank I am not worried).

Both temp gauges under read but as neither overheats I am only going to be worried if they suddenly climb.

Puthijeep oil gauge has a faulty fuse holder in the fuse box and can underread by 40% at times, extra resistance at the fuse contact. Not worrying if you know about it, but it is an unregulated gauge.

You may not have them properly set up but I would use them in that state, just calibrate the arms and remember what says what and how accurate it is. Better than buying new dodgy gauges.

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1981 CJ7 258ci - Bagusjeep
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post #8 of 11 Old 05-27-2020, 10:38 PM Thread Starter
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Quote:
Originally Posted by John Strenk View Post
Did you get a flashing light on the "A" terminal and DID you have a good ground?
John,

I ran a wire from the back of the gauge to the negative side of the battery I'm using, somewhat parallel to the resistors


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post #9 of 11 Old 05-28-2020, 04:32 AM
John Strenk
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Quote:
Originally Posted by Capt_Drake View Post
John,

I ran a wire from the back of the gauge to the negative side of the battery I'm using, somewhat parallel to the resistors
Well check to see if you get a flashing light on the "A" terminal. If not then try cleaning the points a bit with a piece of very fine sandpaper.

If we can't get the "A" terminal to flash, It will be hard to repair.


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post #10 of 11 Old 05-28-2020, 10:39 AM Thread Starter
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I get a very much weaker flash at S then I do at A.

I also procured another gauge, but the wire around the bi-metallic strip is broken, but the "voltage regulator" bit works ok.


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post #11 of 11 Old 05-29-2020, 04:57 AM
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Quote:
Originally Posted by Capt_Drake View Post
I get a very much weaker flash at S then I do at A.

I also procured another gauge, but the wire around the bi-metallic strip is broken, but the "voltage regulator" bit works ok.
That is normal as the "S" terminal has more resistance from the windings around the bi-metalic strip to travel through.

This sounds like it might be salvageable.

There are ways to set the zero position and full scale position.


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