Autometer fuel gauge pegged beyond full? - Team Camaro Tech
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post #1 of 10 (permalink) Old Jun 9th, 12, 03:29 PM Thread Starter
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Autometer fuel gauge pegged beyond full?

I am putting a complete set of Autometer gauges in my car. I have the gauges powered to the IGN terminal on the fuse box. With the key in the OFF position the fuel gauge needle goes all the way to the right until it hits the side of the gauge case. Whet I turn the key to on/ign the needle moves slightly to the left away from the side in the gauge case.

I think I have everything wired correctly but obviously have a problem. Also, the fuel tank is completely dry. No fuel at all.

Matt
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post #2 of 10 (permalink) Old Jun 9th, 12, 07:57 PM
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Re: Autometer fuel gauge pegged beyond full?

is the sending unit stock ??? could be the ground wire that comes off the sending unit !!!
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post #3 of 10 (permalink) Old Jun 9th, 12, 08:05 PM
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Re: Autometer fuel gauge pegged beyond full?

x2 on the ground but it sounds like it is receiving a signal if it moves.
Is the gauge matched for the sender? OEM GM sender is 0-90 ohms. So the gauge has to be matched to be correct. How much fuel do you think is in the tank?


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post #4 of 10 (permalink) Old Jun 10th, 12, 04:56 AM
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Re: Autometer fuel gauge pegged beyond full?

The sounds like the guage is either missing its shunt resistor, the resistor is not the right one for the sender, or the fuel sender circuit is open circuited.

There are two coils of wire inside a fuel gauge one that moves the needle right, and one that moves the needle left. the one that moves the needle upscale (right) always has a fixed amount of current flowing thru it to controlled by the resistance of the wire in the coil and a shunt resistor used to match the upscale current to the downscale current controlled by the fuel sender resistance. If theres no shunt resistor, then the current on the upscale coil will be to high and the gauge will slowly go over to full and then stay there. If the tank is empty (0 ohms) the needle might move back towards E slightly when the key is on.

To test to make sure its not a bad ground on the fuel sender disconnect the fuel gauge sender in the trunck and ground it to the car body, see if the gauge goes to E, if it does then its your sender's ground cable. To test if its the wiring between the gauge and the sender, ground the wire going to the sender right at the gauge, or at the console connector, if the gauge goes to 0 there but not in the trunk then theres a wiring problem between those points.

But it also sounds like your gauges may be wired to a BATT power source, ie one not switched on by the ignition key. There should be no needle movement in either direction with the key off.

Mark Canning
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post #5 of 10 (permalink) Old Jun 10th, 12, 06:22 AM Thread Starter
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Re: Autometer fuel gauge pegged beyond full?

Thanks for the ideas. The sending unit is a new one I bought from Heartbeat City. It said it was for a 67 so I assume it is the right one. I think I hooked the ground up correctly but will take a look and make sure.

Brian, the tank is bone dry. No fuel at all in the tank.

Mark, thanks for the diagnostic tips. I will try those out and see what happens. Where is this shunt resister located? Is there a way I can check to see if it is installed? Can I measure the resistance between the two terminals?

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post #6 of 10 (permalink) Old Jun 10th, 12, 06:55 AM
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Re: Autometer fuel gauge pegged beyond full?

Quote:
Originally Posted by MW67RS View Post
Thanks for the ideas. The sending unit is a new one I bought from Heartbeat City. It said it was for a 67 so I assume it is the right one. I think I hooked the ground up correctly but will take a look and make sure.

Brian, the tank is bone dry. No fuel at all in the tank.
Quote:
Originally Posted by MW67RS View Post


Mark, thanks for the diagnostic tips. I will try those out and see what happens. Where is this shunt resister located? Is there a way I can check to see if it is installed? Can I measure the resistance between the two terminals?


Okay so its a GM sender so look at the gauge paperwork and see if it is already calculated for the GM sender. Most newer aftermarket gauges these days are programmable so you may be able to reconfigure it. If not your options are quite limited. Replace gauge with one for GM sender, or replace sender with Autometer matched one.

The resistor mentioned is required for factory correct reproductions such as the ones made by Classic Headquarters, and not the reproductions made by OER. I don't remember if Autometer gauges ever used one.

You can test the Ohms from the sender to see if it is working. At this point you would be seeing almost zero Ohms from the sender wire in the trunk connection if it is hooked up right. 67-68 are hard to manipulate the float while it is in the tank, 69 you can see it through the filler neck and move it with a bamboo rod.

So you could at this point drop the tank and bench test the sender, or just add fuel to the tank. one Gerry Can - 5 US gals should move you to just above 1/4, or 22 Ohms.


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post #7 of 10 (permalink) Old Jun 10th, 12, 07:04 AM
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Re: Autometer fuel gauge pegged beyond full?

The auto meter gauge should have one built into it if it is specifically for a GM 0-90 ohm sender. GM does use different values on their more modern senders than the older 60-70 vintage cars. As long as the guage is made for a 0-90 sender it should be fine. The guage seems to act like its wired backwards going full scale when the car is off, and only coming slightly off the high scale when the key is off and the tank empty.

Go out to radio shack, buy a 0-100 ohm potentiometer, or a pack of 20, 40, and 80 ohm resistors, disconnect the connector in the trunk, stick one end of each resistor (one at a time) into the connector, and ground the other end to the body. The meter should display rougly 1/4 for the 20, a little below 1/2 for the 40, and about 7/8 for the 80, if its working correctly. You can do the same thing with the pot, just hook it up to the connector in the trunk, ground the other leg and turn the adjustment pin to see the gauge go from empty to full.

Mark Canning
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post #8 of 10 (permalink) Old Jun 10th, 12, 07:41 AM Thread Starter
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Re: Autometer fuel gauge pegged beyond full?

Thanks Mark and Brian. I will try to just ground the wire at first and see if that changes anything. If not I will try the potentiometer.

Matt
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post #9 of 10 (permalink) Old Jun 10th, 12, 07:41 PM Thread Starter
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Re: Autometer fuel gauge pegged beyond full?

I found my problem. There is a connection in the trunk that wasn't made. I must have pulled it out while removing the tank. I plugged it in and the gauge now reads empty like I should. Sorry I didn't find this earlier. Thanks again for the help.

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post #10 of 10 (permalink) Old Jun 10th, 12, 08:29 PM
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Re: Autometer fuel gauge pegged beyond full?

Glad it was just that simple


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