Again another 3 o'clock gas gauge question. - Team Camaro Tech
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post #1 of 3 (permalink) Old Dec 13th, 11, 11:11 AM Thread Starter
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thefley
 
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Again another 3 o'clock gas gauge question.

Ok like i started off in post is I have a 3 o'clock gauge issue, mine worked fine and when I put in about 10 gallons in the car and started the car I noticed that it shows at 3 o'clock position.

so I went to the thread and post copied below and the first problem is I cant find the wire that is suppose to be in the trunk as I think the pan has been replaced.

by reading the post, and knowing I just put fuel in the tank when it putzed up
you would think it would be the unit in the tank? where to start? (note to self go get a volt ohm meter)

Quote:
Common issue with first gens. Easy troubleshooting to isolate if it is the gauge or the sender or the harness.

Unplug the sender lead in the trunk - in a 69 it is the brown single wire connection.
Turn key to on position.
Gauge should read past full.

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.

If it does both of these the gauge is in working condition and harness back to instrument panel is in working order. If not you can test the ohms being sent to the gauge as described below for the sender test, or have a buddy loan you his gauge for a second and plug theirs in and test as above.

If both gauges fail - and your description of your situation sounds as if the gauge is fine to me - the harness may have cracked or broken wire. You can also alligator clip the brown lead of the back of the gauge to a ground to do the above trunk testing to isolate wiring.

But if the gauge moves to past full then past empty with the trunk connector test, then problem is most likely the sender unit in the tank, or its ground.

The sender uses a ground fixed to the back passengers side tank strap and that is where I would start if you can get under the rear you should be able to visually inspect if the wire lead is corroded or loose. If it looks ok and is clean of corrosion it still may not be ok, and you can hook a test lead alligator clip to the connector at the tank strap and then the other end to a new clean ground you have made on the chassis and see if your gauge now reads correct with the key in the run position.

If you have a good ground at the tank or with your new temp ground, you reconnected the lead in the trunk and you still have a past full gauge reading, then maybe the sender unit itself has lost the will to live.

To test the sender you need to test the ohms (resistance) with a simple multimeter.
You measure across the loose lead in the trunk to the connector to the gauge. You
should read anything from 0 to 90 (empty to full). If you are getting something close to what you think is in the tank, the sender maybe ok. You can manually manipulate the float valve with a bamboo rod or wooden dowel through the filler neck. DO NOT USE A METAL ROD. Last thing you want to do is set your tank of gas and your ride, garage and house on fire with a spark. You can also affect change by removing or adding fuel to the tank as you check the ohms.

If you get a change in resistance the sender is most likely ok and the connector in the trunk may have been loose, or the float may have been stuck. if it is flaky better to replace then rebuild in my humble opinion. Dropping the tank is not an easy project without help or a lift and storing gas may not be easy where you live (condo owners take notice your neighbors may rat you out). And if you rebuild, how long would it last before it found its own groove again and left you high and dry.

Hope this helps you find your issue.
Brian
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post #2 of 3 (permalink) Old Dec 13th, 11, 01:50 PM
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Jim
 
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Re: Again another 3 o'clock gas gauge question.

First, try grounding the tank. The gauge wire and the tag light wire both terminate at the same place in the trunk. Trace the tag light wire.
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post #3 of 3 (permalink) Old Dec 13th, 11, 05:16 PM
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Brian
 
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Re: Again another 3 o'clock gas gauge question.

Fly - So even if the new trunk pan wasn't sportin the hole for both the fuel sender lead and the license plate lamp lead, they should both be hanging by the filler door.

What year you having issues with?

In the trunk harness there will be a brown wire that if your sender lead wasn't routed through the trunk floor pan would be missing from. If you ground that connector tot he trunk latch, you will get the results of the test I wrote above. The gauge should go past EMPTY or 9 o'clock. This will confirm that your gauge is capable of translating a signal.

Your next step would be to see if you can locate the brown sender lead from the tank that should have been routed into the trunk but wasn't. If you can find it use a few alligator test leads to patch it into the trunk connector you just used to test with. If the lead can't be found you will need to drop the tank and connect a new lead to the sender.

If you can find it and you connect it and the gauge reads anything but 9 or 3 o'clock all you need to do is drill the hole and feed the lead. Be extra careful using a drill around the tank when its full of gasoline. Don't drill a hole into the tank and set yourself and the ride a blaze.

If you can't get a signal from the sender with alligator clip test leads first double check your connections. If that still fails to read the tank, then leave those in place and under the rear pass side clip a lead from the tank ground on the rear of the strap to a good ground on the body. If that gives you a read, then you need to patch the lead into the tank and cleanup and re-tighten the sender ground at the tank strap.

Brian


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