Gas gauge out by 1/4 tank - Team Camaro Tech
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post #1 of 29 (permalink) Old May 3rd, 15, 02:58 PM Thread Starter
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Gas gauge out by 1/4 tank

I'm have a problem with my '69 gas gauge, I read the sticky and did the tests at the harness in the trunk.

When the harness is unplugged the gauge reads way past full, when the harness is grounded to the trunk latch it reads right at empty but not past it.

I get 49 ohms on my voltage meter which should be between 1/2 and 3/4 of a tank but the gauge reads halfway between 1/4 and 1/2 full.

When I fill up the car at the gas station to the point where gas pours out onto the ground the gauge only reads 3/4 full.

I have console gauges, I haven't removed the gauges to check the ohms at the fuel gauge but since it seems to be under reporting I assume the resistor is working and the gauge must be the problem.

Any advice would be great,

Thanks

Jeff
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post #2 of 29 (permalink) Old May 3rd, 15, 03:17 PM
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Re: Gas gauge out by 1/4 tank

Jeff what are the Ohm's at the back of the gauge? 45 is rough half a tank, 90 is full zero empty.

If the gauge is the right hand instrument pod they can be manually adjusted at the pointer, if console or center pod gauge you have to look at the resistor card on the rear of the gauge.

The resistance card if original is just a thin wire wound around a card and can break changing the results of the gauge.


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post #3 of 29 (permalink) Old May 3rd, 15, 04:36 PM Thread Starter
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Re: Gas gauge out by 1/4 tank

I have console gauges, I'll have to look into how to remove the gauges and check it.

Thanks
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post #4 of 29 (permalink) Old May 3rd, 15, 04:54 PM
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Re: Gas gauge out by 1/4 tank

Just pop the cover of the pod by removing the two front screws and lifting the front edge up. Then run your meter on the brown wire and post. If it is an aftermarket pod by OER or a recent one from CHQ you will not see a rear resistance card or ceramic module. CHQ converted to internal resistors in the past couple years. You can still buy the ceramic modules or craft one with parts from Radio Shack if you find yours damaged or missing.


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post #5 of 29 (permalink) Old May 3rd, 15, 06:21 PM Thread Starter
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Re: Gas gauge out by 1/4 tank

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Originally Posted by 69-Pace View Post
Just pop the cover of the pod by removing the two front screws and lifting the front edge up. Then run your meter on the brown wire and post. If it is an aftermarket pod by OER or a recent one from CHQ you will not see a rear resistance card or ceramic module. CHQ converted to internal resistors in the past couple years. You can still buy the ceramic modules or craft one with parts from Radio Shack if you find yours damaged or missing.


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Hey Brian,

I have original guages, with the wire wrapped around a plate for resistance. I took all the screws out of the console so I could lift the top piece up a bit. I can't get it lifted more then a few inches on the side without it hitting the bottom of the dash or the shift arm.

I see 3 posts, one with a red wire, one black and one brown. I put my meter on the brown post and on the black, I assume the black is a ground but it won't give me a reading.

Is the black a ground? I tried getting ground from the dome light trigger on the door or the screw that holds down the kick plate at the base of the door but I still can't get a reading.

The gas gauge is still working and the trunk harness reads 55 ohms but I can't get it to read from the back of the gauge.

Thanks
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post #6 of 29 (permalink) Old May 3rd, 15, 06:41 PM Thread Starter
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Re: Gas gauge out by 1/4 tank

I got annoyed with looking for a ground so I just put a jumper cable on the negative side of the battery and clipped the other end to my ground on the voltage meter. The only pole that gives me a reading is the black post, it reads about 29 ohms.

The red post and brown post don't give me a reading on the voltage meter.

Thanks
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post #7 of 29 (permalink) Old May 3rd, 15, 08:24 PM
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Re: Gas gauge out by 1/4 tank

"Gas gauge out by 1/4 tank" - I was going to say you got one of the good ones!


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post #8 of 29 (permalink) Old May 3rd, 15, 08:41 PM
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Re: Gas gauge out by 1/4 tank

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Originally Posted by Grifter View Post
I got annoyed with looking for a ground so I just put a jumper cable on the negative side of the battery and clipped the other end to my ground on the voltage meter. The only pole that gives me a reading is the black post, it reads about 29 ohms.

The red post and brown post don't give me a reading on the voltage meter.

Thanks
You are only interested in the Ohms on the brown sender wire. The black is a ground to the console plate. Maybe you disconnected that? Red is power.

You only need to remove the two screws on the top of the pod. The cover is sort of hinged but will lift off up and forward exposing the green gauge pod.

Was your reading of 29 before the resistance card?


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post #9 of 29 (permalink) Old May 3rd, 15, 08:57 PM Thread Starter
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Re: Gas gauge out by 1/4 tank

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Originally Posted by 69-Pace View Post
You are only interested in the Ohms on the brown sender wire. The black is a ground to the console plate. Maybe you disconnected that? Red is power.

You only need to remove the two screws on the top of the pod. The cover is sort of hinged but will lift off up and forward exposing the green gauge pod.

Was your reading of 29 before the resistance card?
The 29 ohms was off the ground post, I get no reading off the brown post, i also tried reading off the harness infront of the gauge pod but got no reading there either.

The odd thing is the gas gauge is working, if there was no resistance at the back of the gauge it would be pegged past full.

I did remove the gauge cover earlier, but was nervousness about removing the gauge from the top incase there wasn't any slack in the wiring. I'll screw the console back together and remove the fuel gauge from the top and see if i can get a reading.

Thanks
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post #10 of 29 (permalink) Old May 3rd, 15, 09:50 PM Thread Starter
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Re: Gas gauge out by 1/4 tank

I took the gauge out from the top, I can't get any ohms reading off the brown wire. The red wire reads 12v.

I have my meter set at 200 ohms and the sending wire in the trunk reads 55 ohms but I get no reading at the gauge.

But if there is no reading for the brown wire at the gauge, why does the gauge still work, the absence of a reading should put the gauge past full.

Thanks
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post #11 of 29 (permalink) Old May 4th, 15, 04:15 AM
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Re: Gas gauge out by 1/4 tank

You are not getting a good reading at the gauge. You should be reading Ohm's through the brown wire connection to the gauge post. It should ballpark the same as the trunk minus a small percentage for the trip from the trunk.

If you are getting that reading then you check the Ohms of the the resistor card. Carefully test end to end without going through the posts. Inspect the original windings for any corrosion or breakage. Post your readings for the card alone. These two tests will determine if the gauge is good or bad and the resistor card is good or bad.


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post #12 of 29 (permalink) Old May 4th, 15, 05:33 AM Thread Starter
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Re: Gas gauge out by 1/4 tank

I have been trying to get a reading from the brown wire with the wire still attached to the gauge. Should I have removed the brown wire from the gauge to get a ohms reading?

Thanks for you help Brian..!
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post #13 of 29 (permalink) Old May 4th, 15, 07:21 AM
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Re: Gas gauge out by 1/4 tank

Yes you want the Ohms from the wire not the gauge.


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post #14 of 29 (permalink) Old May 4th, 15, 02:31 PM Thread Starter
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Re: Gas gauge out by 1/4 tank

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Yes you want the Ohms from the wire not the gauge.
I get 56.8 ohms at the sending unit and 56.6 at the gauge cluster off the brown wire.

How do I test the resistance card?

Thanks
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post #15 of 29 (permalink) Old May 4th, 15, 03:46 PM
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Re: Gas gauge out by 1/4 tank

Sounds like either the gauge and or the resistor.

To test the card: Remove it then one probe at one end and the other on the other side.



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