Another gas gauge questions - Impala Tech
Troubleshooting Diagnosing problems

 
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post #1 of 12 (permalink) Old 03-17-2011, 12:09 AM Thread Starter
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Another gas gauge questions

1963 Impala with 400 SBC & TH350 swap (done by previous owner)

I just finished a complete rewire (American Autowire full kit). When the key is turned on the gauge pegs past FULL. I have the wiring correct to the wire coming up thru the floor, but I haven't yet checked the wiring under the car.

From reading other posts it seems like maybe the sending unit isn't properly grounded maybe? Anything else to check before buying a new sending unit or gas gauge?

The gauge does not move around when driving, it stays on full.
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post #2 of 12 (permalink) Old 03-18-2011, 01:25 AM
 
 
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I am having similar problems with my '61. I have a thread started about it on electrical and troubleshooting. I used a multimeter to check my feed wire from my tank. It read 11 ohms. I checked for voltage at the guage and I had 12 volts. I took the guage out and grounded it directly and the needle never moved. So I am assuming that my gauge is bad based on the result of all of those tests. I hope this helps.

Greg
1961 Impala Sport Sedan
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post #3 of 12 (permalink) Old 03-18-2011, 02:19 AM Thread Starter
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My needle pegs on full when I turn the key on, and falls back to around 3/4 when I turn the key off.
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post #4 of 12 (permalink) Old 03-18-2011, 01:13 PM
 
 
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Ok you might have an issue with your sending unit or maybe a ground.

Greg
1961 Impala Sport Sedan
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post #5 of 12 (permalink) Old 03-22-2011, 01:48 AM Thread Starter
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My sending unit wire is reading 25 ohms
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post #6 of 12 (permalink) Old 03-22-2011, 04:39 AM
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There's a way to check if the sending unit is at fault without dropping the tank. There's a 8 pin connector that connects the Dash harness to the Rear Lamp harness it's left of the head light switch, just above the hand brake lever. Pull apart that plug, you'll find a brown wire in that connector, that's the wire that goes to the fuel sending unit in the tank. Ground the side(brown wire)that goes to the DASH(with the key on) it should go to empty, take off the ground and it should rise(maybe 1/2 maybe more). If the Gauge responds it's ether the brown in the rear lamp harness or the sender. One last thing if you measure 25 ohms in the sending unit the rheostat is good, so the fault is somewhere else. Don't forget you must have 12 volts pos on the plus side of the gauge
Hope this helps julian

1959 El Camino
1963 250 HP SS Impala Convertible
1963 300 HP SS Impala Convertible
1981 Austin Mini Cooper Van
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post #7 of 12 (permalink) Old 03-22-2011, 11:18 PM
 
 
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Seeing I'm here reading, I too am having trouble with the fuel gage in my 62.
Switch is off the gage reads about 3/8's of a tank. When I energise the system the gage pegs to empty. I re-did the ground wire and connection at the tank I ohmed out the wire from tank to gage and it's good.
And yes the tank is full or close to it.
Thanks for any advice.
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post #8 of 12 (permalink) Old 03-23-2011, 02:05 AM Thread Starter
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When I ground the gas gauge wire the gauge reads empty, when I hook it up to the sending unit the gauge reads full all the time.

If I'm understanding the posts correctly that means my sending unit is bad.
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post #9 of 12 (permalink) Old 03-23-2011, 07:24 AM
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Quote:
Originally Posted by Odin View Post
When I ground the gas gauge wire the gauge reads empty, when I hook it up to the sending unit the gauge reads full all the time.

If I'm understanding the posts correctly that means my sending unit is bad.
Not surprising considering it is basically a soldered brass float on a stick activating a rheostat made with a very thin wire wound on a fiber board card, exposed to corrosive chemicals and water that is over forty years old (the factory built it to last at least seven years). They used two different resistance values the newer cars used 90 OHM rheostats and older cars used 30 OHMS.

Big Dave
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post #10 of 12 (permalink) Old 03-23-2011, 10:34 AM Thread Starter
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One more part to order, more dollars to spend, and a real pain in the butt to drop the tank. But I'm used to all that already.
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post #11 of 12 (permalink) Old 03-23-2011, 01:06 PM
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Quote:
Originally Posted by Odin View Post
One more part to order, more dollars to spend, and a real pain in the butt to drop the tank. But I'm used to all that already.
Check the tank for corrosion when it is out (those remote TV cameras on a flexible straw are great for this). The gas tank when not filled with fuel allows water to condensate out of the air which combines with the alcohol in the gas today to form acids which eat the components that where not designed to run alcohol (Jimmy Carter ordered all car manufactures to prepare for alcohol in the fuel back in 1973, but it took them two decades longer to get around to following his executive order).

Only way to stop the corrosion is to keep the tank full all the time or park it in an air conditioned garage.

Big Dave
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post #12 of 12 (permalink) Old 03-23-2011, 02:26 PM Thread Starter
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I suspect corrosion in the tank. I put a glass fuel filter on a couple of weeks ago and it's already full of little particles of crap that looks like maybe rust. I fisgure the in-tank filter disintegrated years ago and who knows what might be in there.
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