Fuel Gauge not working????

[Motor_Head77]

I have a 71' chev and the fuel gauge isnt working right. Its constantly reading empty. I disconnect the wire from the fuse block and it goes up to full. Any suggestions or ideas of what this could be? Im only 21 and this truck is a whole new world for me. I used to always have big jacked up four wheel drives. So i tryin to learn more about this truck. thanx..

[dmack91]

You might want to PM VetteVet and ask - he seems to be the expert on fuel gauges here.

[VetteVet]

Hey I just saw this thread. Here is a good place to start and if you don't solve it we'll go from there. I don't mind PMs but I like to keep the trouble shooting on the forum so that every body can benefit.
http://www.6066gmcguy.org/Electrical-02.htm

[stsalvage]

Me i start checking the wire to the tank its just a negative ground and some time the door chrome still panels that hold down your rubber Matt or your carpet some times it pinches the wire and grounds out the wire.Sence it moves it works on your fuse panel it will say Gas gauge unfused the connector could have some rust on it clean it.

this is kinda different from yours cus its in my 1968 3 door suburban but its the same fuse box

Now the first 2 pictures are of the door still the one at the end is the fuse panel I will start taking pictures on everything on the 3/4 ton and 1/2 ton trucks to have them on file to show what your talking about Now everything i have is done the factory way. If in any way you or some one else has modified it.

Well your on your own

[WILLNIK]

Try checking the float. If it has a hole in it and fills up with fuel, it will sink to the bottom and give you an empty reading. Just my 2 cts.



Terry

[68 Stepside]

Originally Posted by WILLNIK

Try checking the float. If it has a hole in it and fills up with fuel, it will sink to the bottom and give you an empty reading. Just my 2 cts.



Terry

Yep, exactly what I thought too. Sounds like the gauge/wiring is good if you can unhook the wire and the gauge goes up. I'd check to see if you've got a bad float.

[CST10]

Originally Posted by 68 Stepside

Yep, exactly what I thought too. Sounds like the gauge/wiring is good if you can unhook the wire and the gauge goes up. I'd check to see if you've got a bad float.

That's the same issue I had on mine. Float had a hole in it. Replaced it and it's cured.

[lilbluetruck]

Originally Posted by VetteVet

Hey I just saw this thread. Here is a good place to start and if you don't solve it we'll go from there. I don't mind PMs but I like to keep the trouble shooting on the forum so that every body can benefit.
http://www.6066gmcguy.org/Electrical-02.htm

tried your link, but was not working.

Wondering anyone can help me troubleshoot. My sender was replaced 5 years ago. Was working, but my gauge needle was reading on the next set of lines (3oclock) position. Now stopped reading. my tank is completely full, gauge sitting correct now, but at 3/4 tank. I took off the ground and the gauge burries to about 5 oclock. When I put it back on, it goes to 3/4 of a tank. Should I be replacing the gauge or new sending unit. Thank you!

[67 chevelle]

littleblue truck , my guess is your needle has moved , if you ground the brown wire and it goes to 0 , Id adjust it , and go thru a tank , if it does not work corectly , , you sender is probably bad also . You might try posting a new thread as this one is 7 years old , and was for a diferant question

[HO455]

Here is a link to a lot of info on fuel guages by Tbone1964 (who rebuilds guages).

http://67-72chevytrucks.com/vboard/s...d.php?t=640615

[VetteVet]

Originally Posted by lilbluetruck

tried your link, but was not working.

Wondering anyone can help me troubleshoot. My sender was replaced 5 years ago. Was working, but my gauge needle was reading on the next set of lines (3oclock) position. Now stopped reading. my tank is completely full, gauge sitting correct now, but at 3/4 tank. I took off the ground and the gauge burries to about 5 oclock. When I put it back on, it goes to 3/4 of a tank. Should I be replacing the gauge or new sending unit. Thank you!

Your gauge is showing the symptoms of a lack of ground from the sender. You should run a temporary ground wire from a good ground in the cab to the fuel terminal on the fuse panel. It is usually the middle terminal on the end of the panel. Your gauge should go to completely empty with the key on. If it does then you need to find the open circuit on the tan wire that goes to the sending unit in the tank. It's possible that the sending unit isn't grounded to the tank or the tank isn't grounded to the cab.

If you measure the ohms between the sending unit terminal and the tank you should get 90 plus ohms with a full tank. That will tell you if the sender is good.

The fact that your needle is going to the five o'clock position when you remove the ground wire could mean that the gauge isn't grounded in the dash or the gauge resistor is bad.
the link posted by HO 455 will trouble shoot the complete system.

[lilbluetruck]

VETTE, you just brought up a point that I never even would have thought about! You are a genius! Mike fuel tank was removed last year to replace the body mount and I guarantee the body guy did not hook the ground back up from the cab to the tank. Now my question is where would I find that wire and where do I run that wire?

[ncpetersc]

I don't think it's typically a wire. The tank gets grounded through the mounting hardware and brackets clamping it to the cab. You do want to make sure that there is nice clean metal somewhere for the tank to ground to the cab.

[Motor_Head77]

Alright. I will have to check that out. Thanks guys

[Mister laugh]

I'd be willing to bet good money on a bad float. Before you kill yourself tryng to find a new one go down to your local dealer, GM still sells them new and for a very reasonable price.

[Hellfire420]

I have a similar problem, but my gauge stays at half with wires unhooked or not. Is my best bet going to be the gauge itself since it doesn't even move?

[VetteVet]

Doesn't sound like you're getting any power to to the gauge on the pink wire. Or the resistor is bad on the back of the gauge. Check the cluster feed fuse and is anything else not working. BTW it is always a good idea to say what year your truck is.

[Hellfire420]

sorry, it's a 68 chevy c-10, I just took the instrument cluster out and apart, tested the fuel gauge with power like on the link you gave out and it will go up and down. I can't accurately test the resistance cause all I have is a POS multimeter, might see if I can find someone with a good and accurate one, but I noticed that it shows no, or close to it, resistance between any of the connections, even between the fuel gauge and temp gauge, so I wonder if it's a sign of something else wrong. Maybe I'll get it working and my other gauges will start working too, but it's been a long time since I've tinkered with it. I'll keep working on it and check the things you mentioned.

Also, what all is supposed to be coming out of the tank. I remember checking the sender wire for a short or open a long time ago, but I'm also reading about a ground and I don't have anything else on the tank but the fuel line and sender wire. I would assume it's grounded out through the tank itself. Thanks for the help.

[VetteVet]

Originally Posted by Hellfire420

sorry, it's a 68 chevy c-10, I just took the instrument cluster out and apart, tested the fuel gauge with power like on the link you gave out and it will go up and down. I can't accurately test the resistance cause all I have is a POS multimeter, might see if I can find someone with a good and accurate one, but I noticed that it shows no, or close to it, resistance between any of the connections, even between the fuel gauge and temp gauge, so I wonder if it's a sign of something else wrong. Maybe I'll get it working and my other gauges will start working too, but it's been a long time since I've tinkered with it. I'll keep working on it and check the things you mentioned.Here's a guide for you.



Also, what all is supposed to be coming out of the tank. I remember checking the sender wire for a short or open a long time ago, but I'm also reading about a ground and I don't have anything else on the tank but the fuel line and sender wire. I would assume it's grounded out through the tank itself. Thanks for the help.

You'll just have the tan sender wire and it runs to the fuel terminal on the fuse panel. The sender does ground to the tank and the tank grounds to the frame or at least it should. The float operates the variable resistor on the sender which varies the resistance to the fuel gauge and gives the reading on the gauge. If the float is stuck and not moving the variable resistor that would account for no movement on the gauge. Since you said the fuel gauge moved when you removed the wires like the test in the link I posted. I think it may be the problem. If you pull the sender you can test it by connecting the red lead of the multimeter on the sending unit post and the negative lead on the sender body. Then when you move the float arm up and down you should get between zero and ninety ohms. Zero is empty and ninety is a full tank.

[HEADTURNINGC10]

Hey y'all stopping posting before you said how to fix the problem I have a 69 c10 the gauge is stuck at 3:00 but I can't get it to go back up by grounding it but the guy before me put an aftermarket fuse panel I bought the truck with it not working looked at tank and nothing was hooked up at all my gauge is reading 45 ohms post to post I know it's not the spec but does that mean I should replace it the truck is now my daily driver now and if any one can help Id mean alot pictures help colors would help I'm going crazy working on this thing

[Birdman78]

Please help I am having the issue of my fuel gauge going way past full I have replaced both the sending unit and gauge I have no idea where the sending unit leed is supposed to hook to on the fuse box all the wires were painted by the previous owner have just tried to bypass wire harness with no luck and is there supposed to be a third wire on the back of the gauge please help

[VetteVet]

Originally Posted by HEADTURNINGC10

Hey y'all stopping posting before you said how to fix the problem I have a 69 c10 the gauge is stuck at 3:00 but I can't get it to go back up by grounding it but the guy before me put an aftermarket fuse panel I bought the truck with it not working looked at tank and nothing was hooked up at all my gauge is reading 45 ohms post to post I know it's not the spec but does that mean I should replace it the truck is now my daily driver now and if any one can help Id mean alot pictures help colors would help I'm going crazy working on this thing

If you have an aftermarket fuse panel then you may not have the sending unit terminal marked on it. It actually says FUEL on the stock fuse panel. The terminal is located on the right end of the panel in the middle. The sending unit wire is a tan or light brown wire and the fuel gauge power wire is a pink wire at the no.3 pin on the cluster plug.







You may have to run the sending unit wire all the way to the gauge and connect it to the no.4 pin on the cluster plug or to the gauge terminal itself. I have heard of gauge resistor readings all the way to 85 ohms and the gauge still works OK so I would get it reading first and then you might have to replace the resistor to get it accurate depending on what the gauge reads at full and empty.
If you ground the sending terminal on the gauge you should read dead empty.

Originally Posted by Birdman78

Please help I am having the issue of my fuel gauge going way past full I have replaced both the sending unit and gauge I have no idea where the sending unit leed is supposed to hook to on the fuse box all the wires were painted by the previous owner have just tried to bypass wire harness with no luck and is there supposed to be a third wire on the back of the gauge please help

The third terminal on the gauge is the grounding hole for the gauge and no wire goes to it.

[Birdman78]

I do have the stock fuse panel the people who had the truck before me painted everything i even installed a after market fuel guage it does the same thing i cant figure out what is going on i got the sending unit from LMC it reads over 100 ohm's on my meter and i know i dont have a full tank i am just so frustrated and at a loss

[VetteVet]

Your problem is a classic symptom of not having a connection between the sending unit terminal and the sending terminal on the fuel gauge. Have you found the FUEL terminal on the fuse panel yet? I have pointed out it's location above. If it is painted over you might be able to scrape it off and be sure to clean the terminal because the pain may be insulating the connection.

Try to ground this connection and turn on the ignition key and look for the gauge to go to empty. If it does then you have a break in the sending unit wire from the tank. Or the sending unit is not grounded to the tank and frame.

If it doesn't then you have a break between the fuse panel and the gauge. Try grounding the gauge terminal at the gauge. If it still doesn't go to empty then your gauge or resistor is bad or the gauge body is not grounded. If your other gauges and the cluster lights are working then the cluster is grounded.

Go back and read all the posts in the thread and surely you will find the solution.

Cheer up and take a long hard look at what's going on in the world around you. Then ask yourself if a non-working fuel gauge is worth getting frustrated over.

[Birdman78]

I think I found the problem when I replaced my sending unit I didn't notice that they had the sending unit plugged into 12 volt power so I think it fried the sending unit so just ordered a new sending unit and will try that to see how that works and thank you for the input