Fuel Gauge "help needed" - Team Camaro Tech
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post #1 of 9 (permalink) Old Sep 9th, 05, 08:50 PM Thread Starter
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Fuel Gauge "help needed"

I have had problems with my fuel gauge reporting correct. New tank and sending unit. (69 camaro convertible pacer 350/300hp dual fuel lines)
By disconnecting the brown wire coming out of the sending unit, it reports full. Grounding it and it goes to empty. That seems OK. My ground at the fuel tank on the car body should be OK. I wire brushed the area and put a new wire and ground washer on it.
The fuel Gauge still will not go beyond 1/2 full. It will work downward as you drive it; gets down close to empty and it will hold about 6-7 gallons before it is full at the filler neck, buts it will not go beyond 1/2 on the gauge.
I have not pulled the gauge yet or checked the ground at the dash yet. I Will have to pull the radio to have room to get to it.
To me it sounds like the gauge is at fault. Shouldn't that be the case?

I have another used gauge now but not sure if it works. Is there a way to check out this gauge without actually installing it.

1969 Camaro Z-11 Pace Car
350cu/300HP -
Convertible RS/SS- Muncie M20 - posi 3.31, 12 bolt

Last edited by llpainter; Sep 9th, 05 at 08:52 PM. Reason: describe car
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post #2 of 9 (permalink) Old Sep 9th, 05, 10:15 PM
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Re: Fuel Gauge "help needed"

So far, your troubleshooting procedures point to a good gauge. A good way to accurately test the gauge is to get a 100 ohm potentiometer (radio volume control) from Radio Shack. Use an ohm meter to set the pot at 90 ohms. That should get the gauge to read full. From there if you vary the pot's resistance, you should be able to see if the gauge moves smoothly from full (90 ohms) to empty (0 ohms). BTW, all pots have three terminals. Usually, the middle terminal and one of the outer terminals will work.


Larry

Last edited by 69-er; Sep 9th, 05 at 10:16 PM. Reason: reword
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post #3 of 9 (permalink) Old Sep 10th, 05, 07:35 PM
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Re: Fuel Gauge "help needed"

Here's my 0-100 ohm fuel gauge/sender calibration tool - you need to tie the center tap to either outer tap:




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post #4 of 9 (permalink) Old Sep 10th, 05, 07:54 PM Thread Starter
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Re: Fuel Gauge "help needed"

I will get the potentiometer tomorrow.
Could you hook the clamps to the existing fuel gauge wires in the back of the trunk, in series, to check your gauge in the car?
Can you check a fuel gauge that is not mounted in the car? Are does it need to be grounded?
Thanks for the input.

1969 Camaro Z-11 Pace Car
350cu/300HP -
Convertible RS/SS- Muncie M20 - posi 3.31, 12 bolt
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post #5 of 9 (permalink) Old Sep 10th, 05, 08:01 PM
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Re: Fuel Gauge "help needed"

You would REPLACE the sending unit with the pot.

disconnect the brown wire in the trunk, and put one clip on the harness connector it plugged into. Clip the other to a good ground.





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post #6 of 9 (permalink) Old Sep 26th, 05, 06:51 PM Thread Starter
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Re: Fuel Gauge "help needed"

I got the potentiometor and ran a test.

The pot runs ohms from 2.0 to 102. When hooked up to the gauge, the gauge runs empty at the 2.0 ohm and at 102 ohms, it goes up to the same mark the gauge goes to when I fill it up; between 1/4 and 1/2 tank. The ohms meter can move the gauge from there to empty.
I understand the gauges have a two section measuring device and possibility the second section is not working properly.

I have picked up a used fuel gauge. Does someone know how to "bench" hook up the gauge to the potientiometer without installing it in the car?

Where the hot and ground go and where the ohms wires would clip to?

Thanks again,

1969 Camaro Z-11 Pace Car
350cu/300HP -
Convertible RS/SS- Muncie M20 - posi 3.31, 12 bolt
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post #7 of 9 (permalink) Old Sep 26th, 05, 07:08 PM
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Re: Fuel Gauge "help needed"

Quote:
Originally Posted by llpainter
I understand the gauges have a two section measuring device and possibility the second section is not working properly.

I have picked up a used fuel gauge. Does someone know how to "bench" hook up the gauge to the potientiometer without installing it in the car?

Where the hot and ground go and where the ohms wires would clip to?

Thanks again,
The "two section measuring device" sounds like they might be refering to the coils in the gauge. One is the empty coil and the other the full coil. The two coils pull on the pointer and which ever has the most "pull" pulls it towards that side.

Look at my 69 Camaro diagrams. This circuit description below refers to the diagram there. It will help you connect the test leads.
http://www.myimagehosting.com/pic.ph...8aaKnA&i=16287

The FUEL GAUGE is controlled by varying the FUEL GAUGE SENDER resistance.
Current flows from the GAUGES FUSE to the EMPTY coil of the FUEL GAUGE and divides into two paths: 1, through the FUEL GAUGE SENDER to ground and 2, through the FULL coil to ground. These two coils exert a magnetic field on the needle, controlling its position. The gauge is controlled by changes of the FUEL GAUGE SENDER resistance.

When the fuel level rises, the FUEL GAUGE SENDER resistance increases, and less current flows through the FUEL GAUGE SENDER and the EMPTY coil. At the same time, the current in the FULL coil increases. This creates a larger magnetic field that pulls the
needle towards the full side of the gauge.

When the fuel level drops, the FUEL GAUGE SENDER resistance decreases, and more current flows through the FUEL GAUGE SENDER and the EMPTY coil. At the same time, the current in the FULL coil decreases. This creates a larger magnetic field that pulls the needle towards the EMPTY side of the gauge.

Larry
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post #8 of 9 (permalink) Old Sep 28th, 05, 07:32 PM Thread Starter
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Re: Fuel Gauge "help needed"

Thanks for all for the info.
As soon as I can, I will remove the old gauge and try another one.
Larry, that diagram on the instument panel is good for all the gauges.
Will return, hopefully with a gauge that works.

1969 Camaro Z-11 Pace Car
350cu/300HP -
Convertible RS/SS- Muncie M20 - posi 3.31, 12 bolt
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post #9 of 9 (permalink) Old Jan 1st, 07, 03:33 PM
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Re: Fuel Gauge "help needed"

Thanks for the info guys. I think I have my gauge reading accurately now.

Skunk Works
302DZ, M22W Muncie, GV overdrive,12-Bolt Rear 3.73
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Last edited by Andrew69; Jan 1st, 07 at 06:18 PM.
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