gas guage reading - The 1947 - Present Chevrolet & GMC Truck Message Board Network

DanoDMano · 10-28-2003, 12:51 PM

My gas guage when full reads 3/4 tank and when empty goes far below empty.

I know that we have 0-90 ohm sending units. Should it read 0 ohms at empty and 90 when full, or the other way around?

Is there an easy way to calibrate the guage?

Thanks, Dan

71GMC_3/4T · 10-28-2003, 02:01 PM

If the wire is open, it goes waaay past full, so that would be the high (90 ohm) end of it.
When the wire is shorted to ground, it goes to E and that would be the 0 ohm end of it.

I would suggest disconnecting the brown wire at your sending unit. If your guage goes way past full, the guage is probably alright.

You might want to put in a 10 or 20 ohm resistor in series with your sending unit wire and see if that makes it work in the range you want. I don't know what currents are involved, but they should be fairly small to prevent fuel ignition (which would be bad). You can probably get away with a 1/4 watt resistor from Radio Shack, although a 1/2 watt would be easier to work with.

krazy_texan · 10-28-2003, 02:01 PM

i think you have a problem with your gauge mine was doing similar a while back but when full it was reading at 1/4 tank i tried everything, even bought a new sending unit and harness, but it came up to be the gauge.

SWEET7T · 10-28-2003, 02:38 PM

71GMC_3/4T
OOOOoooo.... good call on the resistor!!!! I would go with the 1/2w resistor. I know that not alot of current goes through that wire, but better to have too much, than not enough.

DanoDMano · 10-28-2003, 09:03 PM

Yeah I think that mine is the guage also. It didnt start happening until I installed a new bezel!!

Good advice on raising the resistance for the guage, I think I'll try it. I would like to keep everything to stock specs though. I will be installing an underbed tank someday!!

Thanks for the great advice as usual!!!

10-28-2003, 12:51 PM	#1
DanoDMano Pronounced "Pew-al-up" Join Date: Oct 2002 Location: Puyallup, Washington Posts: 845	gas guage reading My gas guage when full reads 3/4 tank and when empty goes far below empty. I know that we have 0-90 ohm sending units. Should it read 0 ohms at empty and 90 when full, or the other way around? Is there an easy way to calibrate the guage? Thanks, Dan __________________ Classic GM Trucks of Washington Club Member 1970 FS chevy,350/350, Edelbrock cam and intake. Holley 650 carb,HEI,AT,Tangier Orange, 18's, Power Locks, Truck Photos

10-28-2003, 02:01 PM	#2
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	If the wire is open, it goes waaay past full, so that would be the high (90 ohm) end of it. When the wire is shorted to ground, it goes to E and that would be the 0 ohm end of it. I would suggest disconnecting the brown wire at your sending unit. If your guage goes way past full, the guage is probably alright. You might want to put in a 10 or 20 ohm resistor in series with your sending unit wire and see if that makes it work in the range you want. I don't know what currents are involved, but they should be fairly small to prevent fuel ignition (which would be bad). You can probably get away with a 1/4 watt resistor from Radio Shack, although a 1/2 watt would be easier to work with. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

10-28-2003, 02:01 PM	#3
krazy_texan Registered User Join Date: Oct 2002 Location: West Des Moines, Ia Posts: 3,233	i think you have a problem with your gauge mine was doing similar a while back but when full it was reading at 1/4 tank i tried everything, even bought a new sending unit and harness, but it came up to be the gauge. __________________ Krazy Texan My Trucks are made with Wrenches not Chop Sticks 1967 GMC 3/4 ton "Johnny Cash" 1990 v1500 suburban 1967 Ford f100 Swb 4x4 "green bean" GOD BLESS JESUS, JOHN WAYNE, AND THE ALAMO

10-28-2003, 02:38 PM	#4
SWEET7T Try spinnin 4 rear tars Join Date: Sep 2003 Location: Salt Lake City, Utah Posts: 757	71GMC_3/4T OOOOoooo.... good call on the resistor!!!! I would go with the 1/2w resistor. I know that not alot of current goes through that wire, but better to have too much, than not enough. __________________ SWEET7T 1970 C10, 2wd, LB, 307/TH350/3.08. PS, PB

10-28-2003, 09:03 PM	#5
DanoDMano Pronounced "Pew-al-up" Join Date: Oct 2002 Location: Puyallup, Washington Posts: 845	Yeah I think that mine is the guage also. It didnt start happening until I installed a new bezel!! Good advice on raising the resistance for the guage, I think I'll try it. I would like to keep everything to stock specs though. I will be installing an underbed tank someday!! Thanks for the great advice as usual!!! __________________ Classic GM Trucks of Washington Club Member 1970 FS chevy,350/350, Edelbrock cam and intake. Holley 650 carb,HEI,AT,Tangier Orange, 18's, Power Locks, Truck Photos



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