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post #1 of 6 Old 08-09-2020, 07:41 PM Thread Starter
Pappasquat
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the mysterious fuel gauge

85 CJ7.... Would love to have a working fuel gauge. I have replaced the sending unit a while back, and the fuel gauge in the cluster. I did some ohm tests this afternoon.
Fuel Gauge
S-ground 60 ohms
S-I 24 ohms
S-A 25 ohms
A-I 6 ohms
I-ground 48 ohms
A-ground 48 ohms
Also, A-ground measured 16-ish volts at times, and at other times, with some movement of the tester probes, it would pulse on and off around 7 volts.

Temp Gauge
S-A 25 ohms
A-ground pulsed around 7 volts
Any help would be greast, thank you
oh yeah, fuel has pink to S, red to I, temp has purple to S

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post #2 of 6 Old 08-10-2020, 03:55 AM
John Strenk
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Not sure what you mean about a pulsed ground.
There is no ground on the temperature gauge.

What are you using to measure it with. A VOM or a DVM.?


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post #3 of 6 Old 08-10-2020, 11:53 AM Thread Starter
Pappasquat
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So I checked voltage @ both A's and those were the readings
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post #4 of 6 Old 08-10-2020, 11:55 AM Thread Starter
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A VOM
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post #5 of 6 Old 08-10-2020, 01:57 PM
JEEPFELLER
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Garage
So if you have grounded the wire from the fuel sender (or the temp sender) Neither one will rise to the top?

If your gauges are not fried

(maybe just the CVR is shot)

You might get to be the first one on here to try my method! (I'm the 1st, mines been working a long time.)

Maybe my idea might work for you, if it's indeed the gauge being the problem.

Here's a link, keep us posted here.

https://www.jeepforum.com/forum/f8/8...issue-4338415/

I used new gauges with my idea, the new fuel gauge has never been connected to 12 volts (my idea could still work with a used gauge)

If you study my pics, the 12v that used to go to the gauge now powers my "adapter"!

Other than my "Stand In" CVR, the gauges should connect up normally, the speed of the needles movement may be a little slower, you may not even notice.

-----JEEPFELLER
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post #6 of 6 Old 08-11-2020, 04:00 AM
John Strenk
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Quote:
Originally Posted by Pappasquat View Post
85 CJ7.... Would love to have a working fuel gauge. I have replaced the sending unit a while back, and the fuel gauge in the cluster. I did some ohm tests this afternoon.
Fuel Gauge
S-ground 60 ohms
S-I 24 ohms
S-A 25 ohms
A-I 6 ohms
I-ground 48 ohms
A-ground 48 ohms
Also, A-ground measured 16-ish volts at times, and at other times, with some movement of the tester probes, it would pulse on and off around 7 volts.

Temp Gauge
S-A 25 ohms
A-ground pulsed around 7 volts
Any help would be greast, thank you
oh yeah, fuel has pink to S, red to I, temp has purple to S
Quote:
Originally Posted by Pappasquat View Post
So I checked voltage @ both A's and those were the readings
Quote:
Originally Posted by Pappasquat View Post
A VOM
Ah. I understand. You're getting a pulsed 7 volts between the "A" terminal and ground. My brain is a little slow this week.

It seems everything is working on the gauge end.
7 volts is good for a VOM. That is actually why people think it's a voltage regulator in the fuel gauge when it's actually not.
A DVM will give you a pulsing 12 volt signal. So if you were using a DVM and only read 7 volts there may be other problems.

It might be the fuel sensor is not properly grounded or there is something wrong with the sending unit.
I would take the pink wire off the fuel gauge and check the resistance of that plug to the dash ground.
It may be the ground wire on the sensor broke or fell off the sending unit.
Or maybe the wire to the sending unit fell off the terminal on the sending unit or is all corroded inside.

Another quick test would be to simply ground the "A" post and see if the needle moves. It could be jammed against something if it's been replaced.

Also when doing these test make sure the engine is running otherwise if you have a stock ignition system, you could damage the ICM.
It overheats if the ignition is ON and the engine is not running.


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