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#1 |
Active Member
![]() Join Date: Sep 2011
Location: Selah Wa
Posts: 153
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Gas guage problems
71 GMC 2500.
My gas gauge quit working, stayed at 1/2 tank. I unhooked the wire and it went way above full, about the 3 oclock position. I grounded the wire and the gauge went to empty so I figured it was a bad sending unit. When I hooked the wire back up the needle went to between 3/4 and full. I bought and installed a new sending unit still the same problem. I took the sending unit out and hooked the wire up and grounded it, raise and lower the float and the gauge works as it should. Did the same with the old sending unit and it works as it should also. I have tried running a ground wire to it and no change. When either sending unit is installed in tank the gauge reads between 3/4 and full. There is only about 5 gallons of gas in it. I also unhooked wire from fuse box and gauge went to 3 oclock. I am running out of ideas here, hope you guys have some ideas. Sorry for the long post but I wanted to be as specific as possible
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1952 Chev dump truck, 1971 GMC C-20 1950 Dodge Coronet Club Coupe 1972 Plymouth Roadrunner 1965 Buick Skylark GS 1972 Chevy El Camino |
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#2 |
Registered User
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 1,700
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Re: Gas guage problems
On the back of the gauge, there is a resistor mounted between 2 of the posts.. The resistor can't be tested while it is mounted, it has to be removed. Using a voltmeter set to read ohms, test the resistor.. It should be ~ 85 - 90 ohms.. Any more or less, consider it bad..
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#3 | |
Senior Member
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Location: Kansas City
Posts: 496
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Re: Gas guage problems
Quote:
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1971 C10 manual cab. 76 4x4 chassis. Cut short frame. Carbureted Blueprint 350, automatic 700r4. ~ James |
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#4 |
State of Confusion!
![]() ![]() Join Date: Jul 2002
Location: Gulfport, MS USA
Posts: 46,865
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Re: Gas guage problems
Double check the ground on the tank and gauge. Both have to be good for gauge to work correct. I've had to add another ground to my tanckand on another truck added a ground wire to the gauge to correct it.
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Bill 1970 Chevy Custom/10 LWB Fleetside 2010 Toyota Tacoma PreRunner SR5 Double Cab - DD Member of Louisiana Classic Truck Club (LCTC) Bill's Gallery Life isn't tied with a bow, but it's still a gift. Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God! Last edited by Palf70Step; 06-30-2024 at 09:13 AM. |
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#5 |
Registered User
Join Date: Sep 2016
Location: Ft Smith, AR
Posts: 565
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Re: Gas guage problems
On my truck the gauge issue was extra resistance in the fuse block. The fuse box was corroded which added resistance to the circuit.
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#6 |
All stock and staying that way
![]() Join Date: Jul 2003
Location: Elkland, PA
Posts: 1,469
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Either bad tank grounding, or resistance in the wiring harness/connections.
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1970 K/5 Blazer CST 4WD, Bronze, 93k ACT. miles, 350, 4 speed, positraction, 16.5" x 8.25" wheel option, tilt, tach, vacuum, AM/FM, manual throttle...Dad ordered and purchased new 4/70. Currently frame off restoration in progress... ![]() 1972 Cheyenne Super 20 2WD, DK Blue/White, 90K ACT. miles, 402, TH400, 4.10 open, tilt, tach, vacuum, A/C, AM/FM, manual throttle.. A mostly original paint never rusted Texas survivor... ![]() 2017 Sierra 1500 SLT 4WD, Black, 41k miles, 5.3, 6L80E, 3.42 LS, 20" polished wheels, everything but moonroof and 6.2... 2019 Canyon SLT 4WD, White, 60k miles, 3.6, 8L45, 3.23 LS, 18" wheels |
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#7 |
Active Member
![]() Join Date: Sep 2011
Location: Selah Wa
Posts: 153
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Re: Gas guage problems
Thanks for the info.
I know the tank ground is good because that is what I used to test the sending units. I will check the wiring and fuse box for corrosion. I am just having a hard time understanding why everything works fine until the sender is installed in tank. ![]() ![]()
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1952 Chev dump truck, 1971 GMC C-20 1950 Dodge Coronet Club Coupe 1972 Plymouth Roadrunner 1965 Buick Skylark GS 1972 Chevy El Camino |
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#8 |
Registered User
Join Date: Apr 2023
Location: Edmonton,Alberta, Canada
Posts: 50
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Re: Gas guage problems
May have to adjust the angle the float is sitting. Bending the arm of the sender unit to fine tune the reading.
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#9 |
Registered User
![]() Join Date: Oct 2017
Location: Hudson Valley, New York
Posts: 643
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Re: Gas guage problems
Gonna follow along, as my gauge stopped working for no reason. Haven't looked at it yet, but this thread may get me to
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'68 C20 Utility 396 4sp (BuildThread: http://67-72chevytrucks.com/vboard/s...d.php?t=806904 ) '68 C10 50th |
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#10 |
Senior Member
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Location: Alamogordo, NM
Posts: 710
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Re: Gas guage problems
If you're opening and grounding the circuit at the end of the wire that connects directly to the sender then the circuit from the sender to gauge is working properly.
What's interesting is how the gauge winds up being somewhere in the middle when everything is connected. It acts like both senders are stuck in mid-travel. But that seems unlikely. Sure sounds like a ground issue...
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1966 C10 Custom Cab Restomod (Sold) 1969 Camaro Z/28 (Keeper) Current Build: 1968 C10 (Semi-Factory Restoration) 1983 Camaro Z/28 (Next in line, Keeper) 1951 3100 (2nd in line) |
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#11 |
Registered User
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 1,700
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Re: Gas guage problems
Make absolutely certain that both sender float arms aren't hanging up in the same spot inside the tank..
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#12 |
Registered User
Join Date: Sep 2017
Location: Lloydminster Sask Can
Posts: 14
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Re: Gas guage problems
I don’t mean to hijack this post, but I have a 1972 C15 and my gas gauge sits around 1/4 all the time. I can ground it out and the gauge moves as it should. I changed the sending unit last year and replaced my printed circuit on the back of the cluster. Still the same issues persists. Leads me to believe the resistor on the back of the gauge is the culprit. Where can a guy find a new resistor to buy? After reading this thread I can figure out what else the problem could be I am fairly certain you can only install the sending unit one way in these tanks, so I doubt the float is getting hung up. And help or suggestions are appreciated for where I can find a new resistor or if maybe that is not the problem. Thanks everyone.
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1972 GMC Sierra Grande 402 BB TH400 ![]() |
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#13 | |
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Join Date: Dec 2017
Location: Elkhart, Texas
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Re: Gas guage problems
Quote:
https://www.mouser.com/?utm_source=b...Brand%20Mouser Last edited by RustyPile; 07-02-2024 at 06:48 PM. Reason: Add link |
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#14 | |
Registered User
Join Date: Sep 2017
Location: Lloydminster Sask Can
Posts: 14
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Re: Gas guage problems
Quote:
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1972 GMC Sierra Grande 402 BB TH400 ![]() |
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#15 | |
Registered User
Join Date: Dec 2017
Location: Elkhart, Texas
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Re: Gas guage problems
Quote:
Check your inbox, I sent you a PM.... Last edited by RustyPile; 07-06-2024 at 06:19 PM. Reason: Add information |
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