Gas Gauge Issue....Need Help!! - Team Camaro Tech
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post #1 of 13 (permalink) Old Jun 22nd, 09, 06:59 PM Thread Starter
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Gas Gauge Issue....Need Help!!

I've tried everything.....ok there are three prongs on the back of the gauge...viewing from rear....
left stud is sender wire, right is 12v from key, and center is ground.....
when all 3 hooked up, gauge goes to full....
take sender wire off gauge still shows full....
jumper wire from sender prong to middle ground, gauge goes to empty, as it should...i have no idea.

when i perform a continuity check on the gauge, the the key on the sender prong (LH) shows 6 volts (like power is going from right side through the gauge to left side..

I ran a new wire from the sending unit to the gauge, same thing.

with the key on, i can touch the new wire coming off the left side (sender prong) on the gas tank, and it arcs....power is going through the gauge and back to the sending unit..

Any help would be greatly appreciated....gauge seems to work, could it be a bad sending unit?

Need help with this one ASAP, have a guy buying my car this weekend and I cant get the fuel gauge to work..its the original gauge in the dash beside the speedometer.
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post #2 of 13 (permalink) Old Jun 22nd, 09, 07:38 PM
ralph tassone
 
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Re: Gas Gauge Issue....Need Help!!

CHECK THIS LINK http://chevelleengineer.home.comcast...r/fuelgage.htm
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post #3 of 13 (permalink) Old Jun 22nd, 09, 08:05 PM Thread Starter
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Re: Gas Gauge Issue....Need Help!!

thanks i printed that info and will review it tonight.

Thanks again
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post #4 of 13 (permalink) Old Jun 23rd, 09, 03:05 PM Thread Starter
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Re: Gas Gauge Issue....Need Help!!

ok so i have been trying all kinds of stuff, nothing has worked yet...

I can take an ohm reading right at the sending unit and its read around 96.5....tank is not full by the way.....

I can turn the wire on top of the unit 90 degrees and it will read 48..

what the heck is going on??

Need help bad, any suggestions?
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post #5 of 13 (permalink) Old Jun 23rd, 09, 05:27 PM
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Re: Gas Gauge Issue....Need Help!!

OK, basics here. When you disconnect the sender wire from the gauge (tan wire in the trunk under the trunk lock), the gauge should swing to full when the ignition is on. If you then ground that same wire , the gauge should swing to empty. If not, you most likely have an issue with the gauge or the wiring to the gauge. If you are getting different readings from the sender wire on the same tank, I would be suspicious of the fuel sender in the tank. Make sure your connections are good and clean. Also make sure the sender ground is in good shape.

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post #6 of 13 (permalink) Old Jun 24th, 09, 07:59 AM
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Re: Gas Gauge Issue....Need Help!!

To check gauge, viewed from rear -
* Pink wire on right is 12v from key. Confirm with test light
* Tan wire on left goes to sending unit
* Center lug needs good ground. Be sure it's grounded

To test gauge ---------------------
Disconnect tan wire, turn key on, gauge should read full
Connect jumper wire from sending unit (left) terminal to ground, gauge should read empty (with key ON)


Now, (this is my personal revision) go get 40 ohm resistor from Radio Shack and add that into the jumper wire line, and go from sending unit terminal to ground. With key ON, gauge should read about 3/8 of tank. If you're reading about 3/8 tank with that 40 ohm resistor in there, then your gauge is fine. Of course, you don't absolutely need to do the test with the resistor in the line, but I thought it was a real easy way to quickly confirm gauge accuracy.


Now check sending unit---------------

First, make sure wiring looks good. Check ground connection (black wire) and clean.

You can do this on car but you need ohm meter. Go to inside of trunk at center and disconnect gauge (tan) wire. Use ohm meter and take reading from sending unit wire to a good ground. If tank is full it should be about 90 ohms. If tank is bone dry it would read about zero. If it's reading, say, 125 ohms or more, it's no good.

Confirm bad sending unit by draining (or adding) 5 gallons of gas and taking another ohms reading. If you had initial ohms reading of 80 (close to full tank) and you drain 5 gallons of gas, then your ohms reading would drop considerably, maybe to about 55. If your initial ohms reading is close to zero (empty tank) than ADD 5 gallons and it should be around 40 ohms. If you are adding (or draining) gas and the ohms reading is NOT changing, then your sending unit needs to be replaced, or the sending unit wiring simply may be bad (broken wire or bad ground)..................

Dave F. in Rhode Island
'68 Camaro SS Accel DFI 454 (SOLD - I'm a boring Corvette owner now)
Bought my first big-block Chevy in 1970
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post #7 of 13 (permalink) Old Oct 2nd, 09, 01:38 PM
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Re: Gas Gauge Issue....Need Help!!

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Originally Posted by alanrw View Post
OK, basics here. When you disconnect the sender wire from the gauge (tan wire in the trunk under the trunk lock), the gauge should swing to full when the ignition is on. If you then ground that same wire , the gauge should swing to empty. If not, you most likely have an issue with the gauge or the wiring to the gauge. If you are getting different readings from the sender wire on the same tank, I would be suspicious of the fuel sender in the tank. Make sure your connections are good and clean. Also make sure the sender ground is in good shape.

alan
I know this is an old thread.... But my issues are the stock gauge worked fine, i then replaced it with an auto meter for a 69 stock fuel tank/sender.. My buddy hooked all gauges up and all work fine ecept the fuel gauge.

When its fuel the gauge goes past fuel and reads 40-45 ohms with the key on.. When its close to empty it swings down to just beneath 3/4. We read the ohms from the gauge with the key on and it read 40-45 ohms, but with the key off it reads 90-ohms. I'm going to check the rear sending wire but with these symptoms it sounds like the sender is working and a possibility of a bad connection in the trunk sending wire.

Thank you for the help in advance.

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Last edited by Skeeter55; Oct 2nd, 09 at 02:19 PM.
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post #8 of 13 (permalink) Old Oct 2nd, 09, 04:35 PM
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Re: Gas Gauge Issue....Need Help!!

I took off the sending wire from the trunk and the gauge still goes past full. Could he have crossed a couple of wires at the gauge?

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post #9 of 13 (permalink) Old Oct 3rd, 09, 10:24 AM
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Re: Gas Gauge Issue....Need Help!!

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Originally Posted by Skeeter55 View Post
When its fuel the gauge goes past fuel and reads 40-45 ohms with the key on.. When its close to empty it swings down to just beneath 3/4. We read the ohms from the gauge with the key on and it read 40-45 ohms, but with the key off it reads 90-ohms. I'm going to check the rear sending wire but with these symptoms it sounds like the sender is working and a possibility of a bad connection in the trunk sending wire.

Thank you for the help in advance.

Do not check resistance with the circuit live (key on). You also need to realize that since this gauge reading is based off of resistance readings from the sending unit, any abnormal resistance in the circuit is going to affect the reading at the gauge. You need to check the resistance in the wires from the sending unit to the gauge. Wires disconnected from both the gauge and the sending unit, one test lead on one end of the wire another test lead on the other end of the wire. You will be looking for less than 1 ohm of resistance, ideally like .1-.4 ohms. While doing this check the connections them selves, are the conacts clean and tight? A little dielectric grease won't hurt either. Also while the circuit is unplugged at both end check for a short to ground and power on that circuit. One test lead at one end of the wire the other to a good ground, resistance should be very high or out of limits. Then switch it to volts dc with the same hook up with the key on and off there shoud be no volts either time. If the wiring checks out ok then check the sending unit. if you are getting a resistance change from 0 to 90 ohms thru the sweep of the float than thats ok. the only thing left is the gauge is it getting power and good ground? If everything is checking out ok then i would say your gauge is not working properly.

NEVER argue with a stupid person. They bring you down to their level, and then beat you with experience.
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post #10 of 13 (permalink) Old Oct 3rd, 09, 11:29 AM
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Re: Gas Gauge Issue....Need Help!!

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Originally Posted by bighaas79 View Post
Do not check resistance with the circuit live (key on). You also need to realize that since this gauge reading is based off of resistance readings from the sending unit, any abnormal resistance in the circuit is going to affect the reading at the gauge. You need to check the resistance in the wires from the sending unit to the gauge. Wires disconnected from both the gauge and the sending unit, one test lead on one end of the wire another test lead on the other end of the wire. You will be looking for less than 1 ohm of resistance, ideally like .1-.4 ohms. While doing this check the connections them selves, are the conacts clean and tight? A little dielectric grease won't hurt either. Also while the circuit is unplugged at both end check for a short to ground and power on that circuit. One test lead at one end of the wire the other to a good ground, resistance should be very high or out of limits. Then switch it to volts dc with the same hook up with the key on and off there shoud be no volts either time. If the wiring checks out ok then check the sending unit. if you are getting a resistance change from 0 to 90 ohms thru the sweep of the float than thats ok. the only thing left is the gauge is it getting power and good ground? If everything is checking out ok then i would say your gauge is not working properly.
Thank you,

Im going to do all the test in an hour or so and will update what i find or fix.

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post #11 of 13 (permalink) Old Oct 3rd, 09, 04:21 PM
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Re: Gas Gauge Issue....Need Help!!

OK i trouble shot the fuel gauge system and found out that the sender is giving me a reading of 160 ohms at the wire from the sender with it unplugged from the trunk. I mad sure the sender wire was connected to the sender with a flash light and even tried to move it. Same with the ground from the sender to the frame i cleaned it a put it back on the frame.

Well at least im getting a reading past full when full and 3/4 reading when empty.

So how dose a sender go out of whack?

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post #12 of 13 (permalink) Old Oct 7th, 09, 03:58 PM
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Re: Gas Gauge Issue....Need Help!!

possible sulpher deposits on the contacts from the fuel. If your car has ever sat with low fuel level (below sending unit contacts) moisture in tank for long periods of time could also corrode the contacts. since you are checking in the trunk (if i am reading this right) you still have a short piece of wire from the trunk to the sending unit. Your problem could still lie within that wire.

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post #13 of 13 (permalink) Old Oct 7th, 09, 04:39 PM
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Re: Gas Gauge Issue....Need Help!!

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possible sulpher deposits on the contacts from the fuel. If your car has ever sat with low fuel level (below sending unit contacts) moisture in tank for long periods of time could also corrode the contacts. since you are checking in the trunk (if i am reading this right) you still have a short piece of wire from the trunk to the sending unit. Your problem could still lie within that wire.
Thank you for the response,

Thats the wire i was checking before the trunk and after the sender, but it gives me a reading of 160 ohm's n that wire with a full tank and the gauge goes past full.

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