Gas Gauge Trouble - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CalvinF · 02-07-2007, 11:12 PM

I need some advice. Since I bought my '72 the gas gauge has not worked; so I just replaced the sending unit. But the gauge still doesn't read and if you unplug the wire on top of the sending unit (key on) the gauge then goes to full. As soon as I plug it back the gauge goes to empty again. What could be the problem???

*rage'nrat638* · 02-07-2007, 11:16 PM

welcome to the board

byrd · 02-07-2007, 11:27 PM

You probably have a short in the wire between the sending unit and the gauge. You should check for frayed wires or a splice somewhere along the wire. Yu can also just check continuity on the wire if you have a multi meter and BTW Wlecome to the board from KY !!

CalvinF · 02-07-2007, 11:33 PM

Thanks for the welcome. The info on this site has been great! I will try checking the wires as you recomended. Thanks!

*screamin_eagle* · 02-07-2007, 11:41 PM

sounds like my truck field mice made a home out of my truck chewing through random wires. I got all the lights working then quit. if i'm not sure how much gas is in it i just wip out my trusty old dipstick. good luck finding that short

**'68OrangeSunshine** · 02-08-2007, 05:57 AM

I keep a log book. I figure it gets 10 miles per gallon on a 20 gallon tank. That gives me a range of 200 miles. I make sure I fill it again before 200 miles is up.
If it's not the wire, and the sender is new [and assumed to be good] the float could be bad. Leaky, defective or fell off during or after install. Sounds like the gauge is good if it reads (beyond) full when you unplug it.

mnunn454 · 02-09-2007, 09:45 PM

Quote:

Originally Posted by CalvinF

I need some advice. Since I bought my '72 the gas gauge has not worked; so I just replaced the sending unit. But the gauge still doesn't read and if you unplug the wire on top of the sending unit (key on) the gauge then goes to full. As soon as I plug it back the gauge goes to empty again. What could be the problem???

If the gage swings one way when you attach the wire, then another when you remove it, then there's nothing wrong with the wiring or the gage.

Assuming the tank isn't empty (you're sure of this, aren't you?), I think the problem is one of 3 things:

Electrical post on sending unit shorted to ground
Float is sunk or stuck in the down position
variable resister inside the sending unit is bad.

Either way, you'll need to pull the sending unit and head for the bench.

Make sure the float is empty. Then using an ohmmeter, see if the resistance changes as you move the float arm. Check the specs to see what it should read. (0-600 Ohms I think, but don't quote me). Maybe one of our experts with a tech manual can verify.

My guess is the float is sunk, or something's wrong with the sending unit.

Good luck and let us know what you find.

And be careful with that open gas tank. We'd hate to loose a good truck from our collection.

72chevy327 · 02-09-2007, 09:55 PM

any one know what the Ohms should be. i hear it should be 0-90 Ohms.

**clay68c10** · 02-09-2007, 11:46 PM

Yup, 0-90 ohms.
I've seen a new sender read zero, the electrical connector pin wasn't centered in its rubber insulating grommet and was touching the body of the sender (short to ground). It's worth checking.

mnunn454 · 02-12-2007, 09:30 PM

Quote:

Originally Posted by clay68c10

Yup, 0-90 ohms.
I've seen a new sender read zero, the electrical connector pin wasn't centered in its rubber insulating grommet and was touching the body of the sender (short to ground). It's worth checking.

I agree. Just pulled the sending unit out of my setup last weekend and it says 90 Ohms right on it.

Good luck.

**oldgold70c10** · 02-12-2007, 09:49 PM

I've had trouble with some repro floats being too heavy to float. Might be the problem if whole unit is a repro.

**VetteVet** · 02-12-2007, 10:12 PM

http://www.6066gmcguy.org/Electrical-02.htm

02-07-2007, 11:12 PM	#1
CalvinF Registered User Join Date: Nov 2006 Location: Houston Texas Posts: 4	Gas Gauge Trouble I need some advice. Since I bought my '72 the gas gauge has not worked; so I just replaced the sending unit. But the gauge still doesn't read and if you unplug the wire on top of the sending unit (key on) the gauge then goes to full. As soon as I plug it back the gauge goes to empty again. What could be the problem???

02-07-2007, 11:16 PM	#2
rage'nrat638 Account Suspended Join Date: Mar 2003 Location: THE FALL GUY CHICAGO IL Posts: 5,883	Re: Gas Gauge Trouble welcome to the board

02-07-2007, 11:33 PM	#4
CalvinF Registered User Join Date: Nov 2006 Location: Houston Texas Posts: 4	Re: Gas Gauge Trouble Thanks for the welcome. The info on this site has been great! I will try checking the wires as you recomended. Thanks!

02-07-2007, 11:41 PM	#5
screamin_eagle Account Suspended Join Date: Dec 2005 Posts: 114	Re: Gas Gauge Trouble sounds like my truck field mice made a home out of my truck chewing through random wires. I got all the lights working then quit. if i'm not sure how much gas is in it i just wip out my trusty old dipstick. good luck finding that short

02-08-2007, 05:57 AM	#6
'68OrangeSunshine Senior Member Join Date: Feb 2002 Location: Tucson, AZ USA Posts: 7,504	Re: Gas Gauge Trouble I keep a log book. I figure it gets 10 miles per gallon on a 20 gallon tank. That gives me a range of 200 miles. I make sure I fill it again before 200 miles is up. If it's not the wire, and the sender is new [and assumed to be good] the float could be bad. Leaky, defective or fell off during or after install. Sounds like the gauge is good if it reads (beyond) full when you unplug it. __________________ Every 25 years I like to rebuild that 292, whether it needs it or not. Last edited by '68OrangeSunshine; 02-08-2007 at 06:03 AM.

02-09-2007, 09:55 PM	#8
72chevy327 Registered User Join Date: Apr 2006 Location: edmonton ab ca Posts: 88	Re: Gas Gauge Trouble any one know what the Ohms should be. i hear it should be 0-90 Ohms.

02-09-2007, 11:46 PM	#9
clay68c10 Senior Member Join Date: Aug 2004 Location: Centennial, CO Posts: 2,990	Re: Gas Gauge Trouble Yup, 0-90 ohms. I've seen a new sender read zero, the electrical connector pin wasn't centered in its rubber insulating grommet and was touching the body of the sender (short to ground). It's worth checking. __________________ ClusterTruck: 68 C10 Bought in 89, wrecked in 03. Slow low $ rebuild started '17. 6.0 & TKO http://67-72chevytrucks.com/vboard/s...d.php?t=788602 93 K1500 Short Step, 350, NV4500, EBL flash ECU. Vortec heads & roller cam someday... 05 Jeep Wrangler Unlimited. 3” lift & 6-speed 02 E320 the insurance total “free car” 13 Tahoe LTZ

02-12-2007, 09:49 PM	#11
oldgold70c10 Who's got steelies? Join Date: Feb 2006 Location: Morrison, Oklahoma Posts: 1,025	Re: Gas Gauge Trouble I've had trouble with some repro floats being too heavy to float. Might be the problem if whole unit is a repro. __________________ 1969 C10 LWB W/ 250 I6 & 3spd 1970 C10 with '67 small window cab, 68 front end, blue; 305/TH350, 3.08 limited slip rear end, manual brakes, power steering; & 4-wheel drums-My daily driver. 1975 Chevelle Malibu Classic Coupe 350/th350 mint green 1970 C20 Suburban 350/700R4 4.10 gearing green & white 1978 Big 10 Silverado 350/th350, working ac, 2 tone blue-My summer daily driver 1983 GMC 1500 Sierra 305/SM465 2.73 rear end How to add a trip odometer to your 67-72 stock speedometer How to rebuild your Q-Jet My Truck Page My Youtube Channel

02-12-2007, 10:12 PM	#12
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,718	Re: Gas Gauge Trouble http://www.6066gmcguy.org/Electrical-02.htm __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.



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