Fuel Gauge Issue - Team Camaro Tech
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post #1 of 26 (permalink) Old Nov 19th, 17, 08:49 AM Thread Starter
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Fuel Gauge Issue

I have tried to search this issue out, but have not yet found the exact diagnosis procedure. When I turn ignition, the fuel gauge pegs at past full. I checked ground at tank and it meters correct. Sending unit checks 18 ohms when I disconnect the wire from the harness so that seems to be okay (think I'm about 1/8 tank or less). I thought it was a bad gauge, so I bought a new one. Put it in. When I connected battery, the gauge stayed at empty. When I turned key to accessory, the gauge moved slowly to past full. What can I do to test it by making it drop to empty?

Thanks!

Brett........

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post #2 of 26 (permalink) Old Nov 19th, 17, 09:11 AM
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Sounds like a bad sending unit

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post #3 of 26 (permalink) Old Nov 19th, 17, 09:14 AM
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Re: Fuel Gauge Issue

The sending unit range is 90-0 ohms, 90 is full 0 is empty. You can disconnect tan wire at sending unit and your fuel gauge should read empty. You can check gauge by putting a 45 ohm resister between the tan wire and ground of the car, gauge should read 1/2 tank.
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post #4 of 26 (permalink) Old Nov 19th, 17, 09:33 AM Thread Starter
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Re: Fuel Gauge Issue

I feel a little better about already purchasing another sending unit from Summit, but john's post concerns me. I disconnected the tan wire and tried the ignition again and it stayed at past full. How does that confirm the sending unit if it is disconnected?

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post #5 of 26 (permalink) Old Nov 19th, 17, 10:36 AM
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Re: Fuel Gauge Issue

Here is the link to the diagnostic. https://www.camaros.net/forums/1579191-post2.html It's a sticky in the electrical forum.
It has steps that test the gauge function by sweeping the pointer way past full and way past empty.
If you can do that then the gauge is likely in good working order.

If the gauge is sound and the wiring to get to it then the issue is either the ground of the sender or the sender itself.
The diagnostic will eliminate those possibilities.

You don't need to have a potentiometer but they are handy in determining if your resistance wire card or ceramic unit is still good on original style gauges. New gauges are almost always internal resistor these days.

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post #6 of 26 (permalink) Old Nov 19th, 17, 11:47 AM Thread Starter
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Re: Fuel Gauge Issue

Brian,
You did it! I had read that sticky, but it was you directing me to it again and when I re-read it the light bulb came on. It said; "Now ground the end of the harness leading back to the gauge - NOT THE LOOSE LEAD GOING UNDER THE FLOOR TO THE SENDER.
Turn key to on position.
Gauge should read past empty." I Thought; " it says to ground the wire coming from the gauge" Wow! I had read that five times and it wasn't till the sixth time that I got it, duh. I grounded it in each place following it up to the connection under the dash-no workie. I grounded it at the connection going to the console-it worked! So then I pulled the complete harness out of the car, having to disconnect the Orange/White connector at the drivers rear wheel in the trunk. Then I started grounding the tan wire at each spot and the gauge stayed at empty, so I re-connected the harness out of the car-into the connection in the trunk. Turned the ignition to accessory and the gauge moved to 1/8 tank...YEAH!. Now I just don't know what did it. It is a new harness from M&H. I sure am gonna look funny driving around with my front-to-rear harness hanging outside the car flopping around in the wind! jk....
Thanks everyone!

Brett......
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post #7 of 26 (permalink) Old Nov 19th, 17, 11:58 AM
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Re: Fuel Gauge Issue

While there is a lot of good information out there, there is also a lot of mis-information with testing the fuel gauge system and I put together a short video with still pictures when I was testing the system on my 68 Chevy II Nova.

The first minute and a half goes over trunk and tank connections and then after that it gets into what happens when the sender wire is disconnected, then grounded, and then when different values of resistors are used to mimic the resistance the sender inside the tank should have when it's registering the different fuel levels.


Here is some more info further down in this album as to connection issues, how the gauge reads with the gauge shunt in place and then removed, and more:

https://www.flickr.com/photos/121766...57650326895832

Jim
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post #8 of 26 (permalink) Old Nov 19th, 17, 12:11 PM Thread Starter
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Re: Fuel Gauge Issue

Thats a great video. I knew something was up when I grounded the wire and there was no movement to empty. Just need to pinpoint the flaky connection now....

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post #9 of 26 (permalink) Old Nov 19th, 17, 02:39 PM
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Re: Fuel Gauge Issue

Quote:
Originally Posted by Brettallen59 View Post
Brian,
You did it! I had read that sticky, but it was you directing me to it again and when I re-read it the light bulb came on. It said; "Now ground the end of the harness leading back to the gauge - NOT THE LOOSE LEAD GOING UNDER THE FLOOR TO THE SENDER.
Turn key to on position.
Gauge should read past empty." I Thought; " it says to ground the wire coming from the gauge" Wow! I had read that five times and it wasn't till the sixth time that I got it, duh. I grounded it in each place following it up to the connection under the dash-no workie. I grounded it at the connection going to the console-it worked! So then I pulled the complete harness out of the car, having to disconnect the Orange/White connector at the drivers rear wheel in the trunk. Then I started grounding the tan wire at each spot and the gauge stayed at empty, so I re-connected the harness out of the car-into the connection in the trunk. Turned the ignition to accessory and the gauge moved to 1/8 tank...YEAH!. Now I just don't know what did it. It is a new harness from M&H. I sure am gonna look funny driving around with my front-to-rear harness hanging outside the car flopping around in the wind! jk....
Thanks everyone!

Brett......
Willing to bet it is one of the connectors being loose. Try this. While key in the run position, wiggle and knock each connection looking at the gauge. Try to mimic the path it takes from the kick panel back so down, across threshold, up and over wheel well to trunk. You can use painters tape to hold it in plac on top of the interior.

Remember it might take a second or two to register a change on the gauge if its a ohms leak but if you find one of the connectors flakes the connection out and is predicable, double check those wiring connections. You may also find dielectric grease helps maintain the connection by keeping it insulated. On the other side of that connective grease will do the same by making it more connective but less insulated to carrier jump.

Brian


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post #10 of 26 (permalink) Old Nov 19th, 17, 02:57 PM Thread Starter
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Re: Fuel Gauge Issue

Thanks Brian. I have a tube of Dielectric that I'll apply after I do as you recommended.

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post #11 of 26 (permalink) Old Nov 20th, 17, 08:22 AM
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Re: Fuel Gauge Issue

John,

Disconnecting the brown sending wire in the trunk in fact makes the fuel gauge read FULL. It would have been nic(er) of GM to make the gauge read empty, but it doesn't.

So grounding the sending wire should make the gauge read EMPTY?
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post #12 of 26 (permalink) Old Nov 20th, 17, 11:06 AM
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Re: Fuel Gauge Issue

Mike,
My bad , violated basic circuitry 101 ... "complete the circuit".
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post #13 of 26 (permalink) Old Nov 20th, 17, 12:09 PM
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Re: Fuel Gauge Issue

Jeez,

Grounding the fuel sender tan wire ALSO makes the gauge read FULL.

WTH?

I'm interested in getting the gauge to read EMPTY (with gas in the tank) so I can confirm whether or not my low fuel module works.

Maybe I'll try grounding it on another surface.
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post #14 of 26 (permalink) Old Nov 20th, 17, 03:12 PM
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Re: Fuel Gauge Issue

Quote:
Originally Posted by mahunt View Post
Jeez,

Grounding the fuel sender tan wire ALSO makes the gauge read FULL.

WTH?

I'm interested in getting the gauge to read EMPTY (with gas in the tank) so I can confirm whether or not my low fuel module works.

Maybe I'll try grounding it on another surface.
You need to ground the wire that goes forward towards the gauge if the connector is separated. If the plug is separated and you ground the side going to the sender, it will not affect how the gauge reads. Make sure too, you are testing n the proper wire and not on some other circuit.

Also too, I don't know what you are using to ground things or at what point on the car but I have had alligator jumper/test clips that are broken inside and sometimes too, have thought I was touching a wire end or attaching an alligator end jumper/test wire to the chassis ground of the car but in reality I was on top of paint or a film on what looked like bare metal to where an electrical connection was not made just a mechanical one. I've also connected to things that are bolted to other things but again mechanically things were good but there was paint buildup between the two parts and electrically it wasn't good.

If you cannot get the gauge to read empty or below with grounding in the back of the car, then you have to start moving forward towards the gauge to find the issue(s).

Jim
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post #15 of 26 (permalink) Old Nov 21st, 17, 07:13 AM
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Re: Fuel Gauge Issue

The fuel gauge does indeed read EMPTY with the sending wire properly grounded.

I initially thought I grounded the gauge to the fuel filler pipe cover's attachment screw, but this didn't work. I then changed the ground to one of the Phillips head screws for the tail light housing and this proved adequate.

Alas, my low fuel warning light did not come on.
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