Fuel Guage Help Please? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Psycho71 · 03-08-2006, 05:24 PM

I have a 71 long bed. The fuel guage is not working, and I really need it to. I am very good at the mechanical end of vehicles but fall way short when it comes to understanding the electrical workings. I do know basic stuff but have never really been told how the fuel sending unit works.

My thought is; Agiven amount of voltage (12v?) is sent into the sending unit, the float has a wiper that contacts a resistor (or something) that varies the voltage sent back to the guage.

Am I right? If not where am I wrong? Could someone please explain this to me. I promise you will only have to do it once. I have all of the factory components in place (sending unit, and guage). As the wiring in my truck has been severly butchered I will be rewiring the whole truck at some point, just trying to get it to where I can drive it right now.

Any help is appreciated.

Jay

Jayss109 · 03-08-2006, 06:21 PM

I ahve no experience with the stock gauge...but I had problems with my sender... Old sender had holes in the float, and the reostat (resistor) on the sender had a broken wire as well.... Installed a new sender...same problem, always read "E" no matter what. Checked and replaced the ground wire to the tank...no difference. (this was with a new aftermarket gauge)

What I found is the flat, plastic covered wiring that actually goes into the tank and is attached to the sender/float was bad. The Brand new plastic coating has been slighty stripped when I installed it, grounding out the sender signal wire and making it read "E". Check allthe above.

Someone else will be able to tell you about the stock gauge... OR do A search... Ive read about it several times here.

Jason
________
VAPORIZER WIKI

tcoop68 · 03-08-2006, 10:18 PM

Does your needle go all the way to the right or does not do anything?I have found that in the past if it goes to the right its a ground problem.If it does nothing it is a bad connection from the tank or a bad sending unit.Check that out first,it really should'nt be a big problem to fix.

70short/step · 03-08-2006, 10:40 PM

Quote:

Originally Posted by tcoop68

Does your needle go all the way to the right or does not do anything?I have found that in the past if it goes to the right its a ground problem.If it does nothing it is a bad connection from the tank or a bad sending unit.Check that out first,it really should'nt be a big problem to fix.

Mine stays all the way to the right of the gauge about where the 3 would be on a clock. Where is the ground and where does it connect to?
thanks, Perry

Geezer · 03-08-2006, 10:55 PM

The sending unit varies the amount of the ground connection. It shouldn't have voltage to it, as it is the ground. Putting 12 volts to a tank of fuel would scare me! It sounds like the wire came disconnected somewhere.

Huck · 03-09-2006, 10:04 AM

Trace the wire from the tank sending unit back to the firewall. It often breaks or grounds along the rocker or on the floor next to the headlight switch. the other common problem is the float leaks and stays down in the empty position. the mechanics of the sending unit is pretty solid---it varies resisitance to ground via a point on a wrapped potentiometer.
the final possibility is the guage has a small resistor spanning the two contact points--this can go bad but is probably the least likely problem. Let us know what you find~~~.

Brainchild · 03-09-2006, 10:11 AM

Pull the wire of the sender,the gauge should go all the way past full,if it does the problem is in the sender.

Check all the connecting points on hte sender,where the post goes through the connecting ring ect.You can sometims pull the reostat apart,and clean te contacts with some steelwool,and get it to work that way.I have done it several times.You can test operation of hte reostat while you have it apart,which makes it nice.

Psycho71 · 03-09-2006, 06:30 PM

OK, I feel dumb now. I should have known that it would be the ground that was varied, not the voltage.
Thanks for the tips. I after I posted this thread (I will look first next time) I found the thread regarding the "stuck on 1/4 tank" issues and found mine is the same way. So it might also be the resistor in the guage right?

Anyway, I will mess with it and let y'all know what I found.

Thanks again,
Jay

03-08-2006, 05:24 PM	#1
Psycho71 Registered User Join Date: Jan 2006 Location: Kaufman, Tx Posts: 827	Fuel Guage Help Please? I have a 71 long bed. The fuel guage is not working, and I really need it to. I am very good at the mechanical end of vehicles but fall way short when it comes to understanding the electrical workings. I do know basic stuff but have never really been told how the fuel sending unit works. My thought is; Agiven amount of voltage (12v?) is sent into the sending unit, the float has a wiper that contacts a resistor (or something) that varies the voltage sent back to the guage. Am I right? If not where am I wrong? Could someone please explain this to me. I promise you will only have to do it once. I have all of the factory components in place (sending unit, and guage). As the wiring in my truck has been severly butchered I will be rewiring the whole truck at some point, just trying to get it to where I can drive it right now. Any help is appreciated. Jay

03-08-2006, 06:21 PM	#2
Jayss109 Active Member Join Date: May 2005 Location: San Jose, CA Posts: 235	Re: Fuel Guage Help Please? I ahve no experience with the stock gauge...but I had problems with my sender... Old sender had holes in the float, and the reostat (resistor) on the sender had a broken wire as well.... Installed a new sender...same problem, always read "E" no matter what. Checked and replaced the ground wire to the tank...no difference. (this was with a new aftermarket gauge) What I found is the flat, plastic covered wiring that actually goes into the tank and is attached to the sender/float was bad. The Brand new plastic coating has been slighty stripped when I installed it, grounding out the sender signal wire and making it read "E". Check allthe above. Someone else will be able to tell you about the stock gauge... OR do A search... Ive read about it several times here. Jason ________ VAPORIZER WIKI Last edited by Jayss109; 04-27-2011 at 11:36 PM.

03-08-2006, 10:18 PM	#3
tcoop68 tcoop68 Join Date: Jan 2006 Location: Cushing Oklahoma Posts: 226	Re: Fuel Guage Help Please? Does your needle go all the way to the right or does not do anything?I have found that in the past if it goes to the right its a ground problem.If it does nothing it is a bad connection from the tank or a bad sending unit.Check that out first,it really should'nt be a big problem to fix.

03-08-2006, 10:55 PM	#5
Geezer Registered User Join Date: May 2005 Location: Spring Branch Texas Posts: 177	Re: Fuel Guage Help Please? The sending unit varies the amount of the ground connection. It shouldn't have voltage to it, as it is the ground. Putting 12 volts to a tank of fuel would scare me! It sounds like the wire came disconnected somewhere. __________________ If you can't drive it park it! If you can't park it milk it!

03-09-2006, 10:04 AM	#6
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,261	Re: Fuel Guage Help Please? Trace the wire from the tank sending unit back to the firewall. It often breaks or grounds along the rocker or on the floor next to the headlight switch. the other common problem is the float leaks and stays down in the empty position. the mechanics of the sending unit is pretty solid---it varies resisitance to ground via a point on a wrapped potentiometer. the final possibility is the guage has a small resistor spanning the two contact points--this can go bad but is probably the least likely problem. Let us know what you find~~~.

03-09-2006, 10:11 AM	#7
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	Re: Fuel Guage Help Please? Pull the wire of the sender,the gauge should go all the way past full,if it does the problem is in the sender. Check all the connecting points on hte sender,where the post goes through the connecting ring ect.You can sometims pull the reostat apart,and clean te contacts with some steelwool,and get it to work that way.I have done it several times.You can test operation of hte reostat while you have it apart,which makes it nice. __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

03-09-2006, 06:30 PM	#8
Psycho71 Registered User Join Date: Jan 2006 Location: Kaufman, Tx Posts: 827	Re: Fuel Guage Help Please? OK, I feel dumb now. I should have known that it would be the ground that was varied, not the voltage. Thanks for the tips. I after I posted this thread (I will look first next time) I found the thread regarding the "stuck on 1/4 tank" issues and found mine is the same way. So it might also be the resistor in the guage right? Anyway, I will mess with it and let y'all know what I found. Thanks again, Jay



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