gas gage is pegged
Thread Starter
Racer
Joined: Aug 2011
Posts: 429
Likes: 24
From: Charlotte NC
gas gage is pegged
After reinstalling and connecting the fuel sending unit I reconnected the battery and then turn the ignition switch to ON. I then noticed the fuel gage to be fully pegged and after disconnecting everything again it remains in the peg position. So I need to reset it and correct what may have caused it. Any ideas?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
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From: Cool Northern Michigan
No expert on gauges but I seem to recall an old phrase that when any gauge is pegged, wither its gas gauge, voltage, oil or water temp gauge, it means its not grounded properly. In other words, no resistance because of no complete circuit.
Thread Starter
Racer
Joined: Aug 2011
Posts: 429
Likes: 24
From: Charlotte NC
Yes thanks, I was just reading that on someone else post who is also having gage problems. I think I might be short circuiting the ground on the lock ring on the fuel sending unit and that might have the same result. Probably should take picture of it and post it on here. Thanks
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
H-m-m-m. Not sure. But to me a short circuit is positive to ground, resulting in sparks, blown fuses and the like. I think your gauge is getting 12V but is NOT getting a good ground. But where? IDK
The gauge right out of the box was at zero / empty correct? Then you hooked it up and it pegged?
The gauge right out of the box was at zero / empty correct? Then you hooked it up and it pegged?
Safety Car
Joined: Apr 2015
Posts: 4,890
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From: Jackson MS
Fuel gauge pegged at FULL indicates a missing Ohm signal from the sender.
Here's a link to the Willcox site.
http://repairs.willcoxcorvette.com/1...-can-tell-you/
Here's a link to the Willcox site.
http://repairs.willcoxcorvette.com/1...-can-tell-you/
Safety Car
Joined: Oct 2015
Posts: 4,782
Likes: 223
From: Lebanon Pa
Fuel gauge pegged at FULL indicates a missing Ohm signal from the sender.
Here's a link to the Willcox site.
http://repairs.willcoxcorvette.com/1...-can-tell-you/
Here's a link to the Willcox site.
http://repairs.willcoxcorvette.com/1...-can-tell-you/
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Thread Starter
Racer
Joined: Aug 2011
Posts: 429
Likes: 24
From: Charlotte NC
H-m-m-m. Not sure. But to me a short circuit is positive to ground, resulting in sparks, blown fuses and the like. I think your gauge is getting 12V but is NOT getting a good ground. But where? IDK
The gauge right out of the box was at zero / empty correct? Then you hooked it up and it pegged?
The gauge right out of the box was at zero / empty correct? Then you hooked it up and it pegged?
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Resets the gauge? I would think when power is truely removed, the needle should go to empty, I guess. So now I wonder if that circuit truely does go dead when you turn the IGN off. Now I suspect the sending unit instead of the gauge.
So the new question is how does a fuel tank sending unit ground itself? Maybe trace the wiring back from the tank as far as GM will allow you too before its hidden.
Somebody else might know more about this and chime in.
So the new question is how does a fuel tank sending unit ground itself? Maybe trace the wiring back from the tank as far as GM will allow you too before its hidden.
Somebody else might know more about this and chime in.
Safety Car
Joined: Apr 2015
Posts: 4,890
Likes: 202
From: Jackson MS
The needle moves according to the variable resistance signal from the sending unit.
If your C3 is 1978 - 1982, the signal wire is pink going into the gauge cluster.
For 1977, this wire is tan.
(I'm not familiar with the wire colors on other years)
Check this wire's continuity between the gauge and the in-tank sending unit.
If the wire is securely attached to the gauge and also the sending unit with good continuity, the sender is bad.
Here's another link to the Willcox site with a video about troubleshooting the fuel gauge.
http://repairs.willcoxcorvette.com/1...el-gauge-test/
Edit: I don't see any wires attached to the sender in the photo you show in post #5.
This wire should run to the driver's side of the tank and into a harness behind the driver side rear wheel.
Also clarified the comment about signal wire color.
Last edited by wendellp601; Nov 15, 2019 at 03:08 PM. Reason: Added info
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
If his gauge is still in the cluster, it would be tough to get a jumper lead to it. Got any other ideas to test the circuit? I believe the gauge is ok, but his first post says new sending unit.
Where does the sending unit ground itself?
Where does the sending unit ground itself?
Last edited by HeadsU.P.; Nov 15, 2019 at 03:14 PM.
Safety Car
Joined: Apr 2015
Posts: 4,890
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From: Jackson MS
The signal wire attaches to the terminal at 9 o'clock.
Thread Starter
Racer
Joined: Aug 2011
Posts: 429
Likes: 24
From: Charlotte NC
I had disconnected the wires in the photo thinking the fuel gage would go back to zero but apparently not. I'll disconnect the battery now and see what happens. I need to connect an ohm meter and check results but not today it's too cold I'll wait for better weather haha. Thanks for your help!
Safety Car
Joined: Apr 2015
Posts: 4,890
Likes: 202
From: Jackson MS
I had disconnected the wires in the photo thinking the fuel gage would go back to zero but apparently not. I'll disconnect the battery now and see what happens. I need to connect an ohm meter and check results but not today it's too cold I'll wait for better weather haha. Thanks for your help!
If this test is OK, the problem is in the signal wire.
I've had a flaky connection at the terminal at 9 o'clock before that caused this.
Race Director
Joined: May 2006
Posts: 18,755
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Did you at some point twist the outlet pipe on the sender during removal or installation to cause that contact with the ground tab.
If you did and the pipe can be twisted by hand you broke the solder joint and the sender will leak.
If you did and the pipe can be twisted by hand you broke the solder joint and the sender will leak.
Thread Starter
Racer
Joined: Aug 2011
Posts: 429
Likes: 24
From: Charlotte NC
No I didn't lay a finger on that. Just used a screw driver to push the lock ring off and then on again at install. Did not replace the sending unit.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
A quick and dirty test I used back in my dealer tech days- nobody seems to agree and thinks I'm full of s***, but it works. 12v test light with an 1893 bulb. Disconnect the sender and put the test light from the wire to a ground. Key on, test light will just barely light up, but the indicator will go to about 1/2 tank. Unless the gauge is bad. Works for temp gauge too. When you're working flat rate money, all the quick tricks you can come up with make you more cash......
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
A quick and dirty test I used back in my dealer tech days- nobody seems to agree and thinks I'm full of s***, but it works. 12v test light with an 1893 bulb. Disconnect the sender and put the test light from the wire to a ground. Key on, test light will just barely light up, but the indicator will go to about 1/2 tank. Unless the gauge is bad. Works for temp gauge too. When you're working flat rate money, all the quick tricks you can come up with make you more cash......
(drum / cymbal roll please)
Last edited by HeadsU.P.; Nov 16, 2019 at 04:21 PM.