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Old 05-08-2014, 02:55 PM
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Checking sending unit in 68 Camaro with multiple meter

Hi, I'm trying to get everything up and going on my 68 Camaro. I've had it less than a year and the previous owner had hacked up some of the wiring.

The fuel gauge has never worked, the needle was pointing straight down. I have an extra gauge that I swapped in. It will read past full when the tan wire is unhooked and past empty when the tan wire is grounded. So far I think this gauge is ok. It just shows past full when everything is hooked up correctly.

On to the sending unit. The ground wire is new so that area is ok. From what I've researched you can hook an ohm meter to the sending unit and it should show 90 if it's full and 0 if it's empty. I have a digital multimeter and I'm not sure if I'm doing everything right. Do I touch the red lead from the meter to the tan wire to the sender and then ground the black wire from the meter? I'm sure the red lead goes to the tan wire which is the wire coming up from the dash. I'm not sure where I touch the black lead from the meter.

One last question, the meter has several settings to measure ohms. A 20M, 2M, 200k, 20k, 2k, and 200. Do I choose 200?

Any help would be appreciated! I'm no wizard when it comes to diagnosing electrical components.

Thanks again!

Joe

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Old 05-08-2014, 04:43 PM
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Originally Posted by 4speed57 View Post
HI have a digital multimeter and I'm not sure if I'm doing everything right. Do I touch the red lead from the meter to the tan wire to the sender and then ground the black wire from the meter? I'm sure the red lead goes to the tan wire which is the wire coming up from the dash. I'm not sure where I touch the black lead from the meter.

One last question, the meter has several settings to measure ohms. A 20M, 2M, 200k, 20k, 2k, and 200. Do I choose 200?
Since the only power used during the test will be coming from the multimeter, it doesn't matter which test lead goes to which - you're just measuring resistance and there is no polarity. As for the scale, yes, use the 200 ohm scale. When measuring resistance, you want to use the lowest scale that won't peg the meter to get the best accuracy. If you don't know the resistance, start higher then keep switching to a lower scale. This is less critical when checking resistance than when checking voltage, for example, as you won't harm the meter if you pick the wrong scale for resistance.
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Old 05-08-2014, 06:17 PM
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X2 with what Joe posted.

How are you doing your sweep test?
Is the tank/sending unit out of the car?

Normally the gauge reading past full indicates the tan wire isn't seeing a ground via the sending unit. So it's one of three things.....

1. Tan wire is broken, test continuity by using a multi-meter with one probe at the gauge and the other, via a long jumper wire, at the sending unit.

2. You posted "the ground wire is new so that isn't the issue"....... It might be the issue. Take a pair of vice grips and attach a temp ground wire to a known good ground point....like the bumper. use a screw driver or other suitable scraping device a scrape the crud from the center area of the actual sending unit, not the mounting flange nut or tank, hold the other end of the temp jumper wire to the scraped off area and see if the gauge works correctly

3. The sending unit, probably need to remove it from the tank to do a sweep/range of motion ohm test.
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Old 05-08-2014, 07:00 PM
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Thanks for the replies and help guys! The sending unit is still in the tank. When I get home in a couple of hours I'll do some more checking.

Thanks again!
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Old 05-08-2014, 07:14 PM
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Do you know where to access the top of the tank?
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Old 05-08-2014, 10:54 PM
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Too bad it's right on top of the tank. One car I had it was on the end close to the rearend. Made it easy to access the wires.

Last edited by 4speed57; 05-08-2014 at 11:02 PM.
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Old 05-08-2014, 10:56 PM
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I had the tank off a few months ago, the wires look ok. I was going to take it back off today, but it's full of gas.

I put an abrasive wheel on my drill and scuffed the other side of the tank strap, across from the original ground wire. I drilled a small hook and grounded the new wire with a screw and washer.

Thanks!

Last edited by 4speed57; 05-08-2014 at 11:06 PM.
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Old 05-08-2014, 11:47 PM
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I just tried again to get a reading on the multimeter. I couldn't get anything at all coming from the sender. Does that mean it's bad? I've heard the range is 0-90 and mine may be 0. With a dead sender should it show anything? I would say the tank is at least half to 3/4 full.

Thanks again!
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Old 05-09-2014, 04:44 AM
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If the sender isn't getting a ground it will not read anything..... and the sender may be good and the ground might be bad. You might be able to disconnect the filler neck, loosen the straps and drop the tank down a couple of inches to get access to the top of the sender. Try scraping an area with a long screwdriver on top of the sender etc.......

If you decide to drop the tank, stuff a rag in the filler neck, place a piece of plywood on a floor jack and let it down slowly..... done a few that way, works pretty well.
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Old 05-09-2014, 12:47 PM
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Thanks EOD guy, I will give that a shot. I need to be sure the sender is bad before I buy a new one. I've been down that road before!

Thanks!
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