Gas gauge not working - Vintage Mustang Forums
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post #1 of 11 (permalink) Old 03-16-2019, 08:39 AM Thread Starter
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Gas gauge not working

I have a few issues with my 65 but this one stumps me. The previous restore installed a new gas tank and im assuming a new sending unit . Any other suggestions to explain my dilemma?
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post #2 of 11 (permalink) Old 03-16-2019, 09:00 AM
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Turn the key ON. Remove the wire from the sending unit. Touch the wire to a good ground. The gauge should go to F rapidly.
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post #3 of 11 (permalink) Old 03-16-2019, 09:44 AM
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If it goes full rapidly, problem is in sending unit.
If it does not, problem is in wiring or gauge head in dash.
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post #4 of 11 (permalink) Old 03-16-2019, 11:08 AM
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When you say it’s not working, do you mean at all or that it’s just not accurate? Apparently after-market sending units are crap and none are accurate.

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post #5 of 11 (permalink) Old 03-17-2019, 10:24 PM Thread Starter
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Not working at all I took the wire off at the tank and tried
testing with a voltmeter got no reading.
post #6 of 11 (permalink) Old 03-17-2019, 11:06 PM
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Originally Posted by [email protected] View Post
Not working at all I took the wire off at the tank and tried
testing with a voltmeter got no reading.
A voltmeter won’t help there. This is very little voltage across that line. The way the system works the resistance of the sender is what matters. 5V comes from the constant Voltage regulator. It goes to the gauge, then from the gauge to the sender it passes through the sender and grounds through the tank to the body. As the sender moves down the resistance increases reducing the flow through the gauge and the needle falls. If you are getting no movement of the gauge you have a few possibilities.

1. The CVR is bad, but then your temp sender would be dead too.
2. The wiring is bad or loose
3. The sender is bad. As said earlier, if you ground the wire at the sender the gauge should go rapidly to full. Don’t leave it connected as you could damage the gauge
4. The gauge is bad.

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post #7 of 11 (permalink) Old 03-18-2019, 12:26 AM
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Went thru the same thing on my "new" Emberglo 66. I used a jumper wire on the end of the plug that goes on the sending unit and used a test probe for continuity until I figured out there was a break in the wire that was wrapped in the harness as it passed thru the trunk in front of the gas tank. Maybe something heavy mashed it years ago... The CVR voltage pulses so it did me no good to try to use a digital voltmeter, only an old school analog needle sweep voltmeter will bounce accurately with the pulse.

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post #8 of 11 (permalink) Old 03-18-2019, 09:29 AM Thread Starter
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So my temp gauge is out as well so ill try replacing voltage reg.
post #9 of 11 (permalink) Old 08-10-2019, 04:50 PM Thread Starter
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Finally got around to it and replaced vr and gas guage works. However temperature guage goes past hot within 5 min of driving time. Thoughts?
post #10 of 11 (permalink) Old 08-10-2019, 05:31 PM
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Get a cheap electric gauge with numbers, or an infrared thermometer and check various areas around your engine when it's warmed up and see if it's running hot.

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post #11 of 11 (permalink) Old 08-10-2019, 07:16 PM
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"im assuming a new sending unit "

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