How to find why fuel gauge doesn't work?

[vikingsandpintos]

Getting some more stuff knocked out on my daughters 67 C10...

The fuel gauge reads empty, and didn't change when I put fuel in it. The wire going to the sending unit from the dash and under the carpet and seat is hooked up. What is the best way to figure out what isn't working? It could be sending unit, gauge, or wiring, just not sure how to diagnose it all. Any suggestions are appreciated, thanks! Earl

[demian5]

Pull the wire off the sender, turn the ignition on and ground the wire to the body. It should go to full.

- If it doesn't move, try it at the gauge terminal (connect to ground). If it moves at the gauge, then you know the wire has an open (you say empty, but if the gauge was showing full then I would tell you it may have a short to the vehicles body).
- If the gauge goes full AND the wire is good, the sender is easy enough to pull and take a look at. Make sure it is grounded to the tank and the tank is grounded to the body. A simple DVOM resistance check between components can show that.
- If the gauge doesn't do squat, check the power to it .
* If it has power, check that the resistor on the gauge isn't blown. I've seen many a gauge replaced for a $2 resistor that can be replaced! They are sold through truck and car shop.
* If it doesn't have power, well, figure out why or jumper power to the gauge directly (at least jumper to figure out if the gas gauge or sender is working).

[ApacheIvan]

Originally Posted by demian5

Pull the wire off the sender, turn the ignition on and ground the wire to the body. It should go to full.

- If it doesn't move, try it at the gauge terminal (connect to ground). If it moves at the gauge, then you know the wire has an open (you say empty, but if the gauge was showing full then I would tell you it may have a short to the vehicles body).
- If the gauge goes full AND the wire is good, the sender is easy enough to pull and take a look at. Make sure it is grounded to the tank and the tank is grounded to the body. A simple DVOM resistance check between components can show that.
- If the gauge doesn't do squat, check the power to it .
* If it has power, check that the resistor on the gauge isn't blown. I've seen many a gauge replaced for a $2 resistor that can be replaced! They are sold through truck and car shop.
* If it doesn't have power, well, figure out why or jumper power to the gauge directly (at least jumper to figure out if the gas gauge or sender is working).

Perfect explanation! You can do this with oil or temp gauge as well.

[vikingsandpintos]

Wow, that was fast! Thank you, this forum is awesome... Lots of helpful people here! I would encourage everyone to become a member to help support this, what an asset to the Chevy truck community!

[RenoKeene]

Could be as simple as the float. I'm on my third aftermarket one now. They are so poorly made that ethanol eats holes in them. One of them actually split but not at the seam!

[71CHEVYSHORTBED402]

Originally Posted by RenoKeene

Could be as simple as the float. I'm on my third aftermarket one now. They are so poorly made that ethanol eats holes in them. One of them actually split but not at the seam!

Word is these are good float replacements: Jeep OMX-1772901 (a.k.a. 17729.01).

The gauge in my driver doesn't work right. Actually, I witnessed it register for a second, when it was cold as heck. It works well enough for me. Reads a pinch over 1/4 when full. At 1/8 it's time to fill up again.

[demian5]

Originally Posted by 71CHEVYSHORTBED402

Reads a pinch over 1/4 when full. At 1/8 it's time to fill up again.

Sounds like your resistor is bad. My sons 86 operated like that, turned out the resistor on the rear of the gauge was bad.

[RenoKeene]

Originally Posted by 71CHEVYSHORTBED402

Word is these are good float replacements: Jeep OMX-1772901 (a.k.a. 17729.01).

The gauge in my driver doesn't work right. Actually, I witnessed it register for a second, when it was cold as heck. It works well enough for me. Reads a pinch over 1/4 when full. At 1/8 it's time to fill up again.

I'll check it out, thanks.

[Cmillet]

Originally Posted by 71CHEVYSHORTBED402

Word is these are good float replacements: Jeep OMX-1772901 (a.k.a. 17729.01).

The gauge in my driver doesn't work right. Actually, I witnessed it register for a second, when it was cold as heck. It works well enough for me. Reads a pinch over 1/4 when full. At 1/8 it's time to fill up again.

That plastic Jeep float on Amazon fixed my problems!

[Canuckvetter]

Originally Posted by RenoKeene

Could be as simple as the float. I'm on my third aftermarket one now. They are so poorly made that ethanol eats holes in them. One of them actually split but not at the seam!

Mine did the same always on empty. Float had a pin hole in it. Changed that 2 yrs. ago. No issues.

[Coley]

Originally Posted by Canuckvetter

Mine did the same always on empty. Float had a pin hole in it. Changed that 2 yrs. ago. No issues.

ditto on the float....and easy to check. I've had a few go bad and lose their buoyancy.
Just move the seat forward and carefully remove the sending unit. if the float feels 'heavy'...its full of gas from a pin hole or a crack.

Coley

[demian5]

Originally Posted by ApacheIvan

Perfect explanation! You can do this with oil or temp gauge as well.

Fuel and temp gauge for sure, but the oil gauges are mechanical in these trucks from the factory from what I have seen.

[jojomiamia]

Hi,

I bought an aftermarket sending unit to go with a brand new tank, float was full of fuel two weeks later...reading 0

[ApacheIvan]

Originally Posted by demian5

Fuel and temp gauge for sure, but the oil gauges are mechanical in these trucks from the factory from what I have seen.

True dat! I forgot

[demian5]

Originally Posted by demian5

Pull the wire off the sender, turn the ignition on and ground the wire to the body. It should go to empty.

- If it doesn't move, try it at the gauge terminal (connect to ground). If it moves at the gauge, then you know the wire has an open (you say empty, but if the gauge was showing full then I would tell you it may have a short to the vehicles body).
- If the gauge goes full AND the wire is good, the sender is easy enough to pull and take a look at. Make sure it is grounded to the tank and the tank is grounded to the body. A simple DVOM resistance check between components can show that.
- If the gauge doesn't do squat, check the power to it .
* If it has power, check that the resistor on the gauge isn't blown. I've seen many a gauge replaced for a $2 resistor that can be replaced! They are sold through truck and car shop.
* If it doesn't have power, well, figure out why or jumper power to the gauge directly (at least jumper to figure out if the gas gauge or sender is working).

The original poster never came back to say he fixed anything.

You should start here and report back.

[Freestate]

Originally Posted by demian5

The original poster never came back to say he fixed anything.

You should start here and report back.

I think I'll start with looking at the float. I have a gut feeling its that, then I will work through this process if that's not the fix. Thanks for the help!

[demian5]

Originally Posted by Freestate

I think I'll start with looking at the float. I have a gut feeling its that, then I will work through this process if that's not the fix. Thanks for the help!

Work smarter, not harder.

Pull the wire off the sender, turn the ignition on and ground the wire to the body. It should go to full.

[VetteVet]

Originally Posted by demian5

Work smarter, not harder.

Pull the wire off the sender, turn the ignition on and ground the wire to the body. It should go to full.

High resistance equals more fuel and low resistance equals less fuel. Grounding the wire will give less resistance. I think you will find the gauge will read empty.

Remember, when the tan wire is off the sender the gauge reads past full because of the high resistance to ground AKA infinity between the wire and ground.

The temperature gauge works just the opposite, when you ground the sender wire the gauge goes to full HOT. Perhaps you had them mixed up.
I have done it myself, because they are so similar. VV

[mike16]

pulling my fuel tank out due to serious rust issues, pulled out the sender and discovered that the rheostat switch inside attached to the sender inside the tank was completely rusted away, the lever that attaches to the float, the float itself and the sock filter... all gone. maybe its that junk that keeps clogging my filter every 4 days. Pull your intank sender unit. you may be surprised.

[VetteVet]

read this thread, it will solve fuel gauge issues.

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

[Coley]

Another thing that can get the gauge out of whack is with a second fuel tank that may have its own sending unit. I have one of those on my truck and there is a toggle switch for it under the dash.
The tank has not been used in, I suppose 10 years...but my buddy flicked that toggle switch to see what it would do out of curiousity.
Well the gauge headed for the 3:15 position which confused me at first because he didn't tell me about flicking the toggle switch.
However, something in that extra fuel system...perhaps a second sending unit in the other tank?....shut off my primary tanks connection and I lost my fuel gauge until I clicked the switch back.
Easy stuff.....just have to keep track of things.

all good
Coley

[Freestate]

I'm going to piggy off of this thread as I'm having similar issues. I have not started diagnosing the problem but wanted to see if I could get some expert advice as to where I should start.

Issue: When the gas tank is full, the fuel gauge will read just barely over 1/4. As the tank gets empty, it will drop to 1/8. I've never let it get below that before filling. My first thought would be to check the float. Thoughts? Should I check something else first before pulling the float out?

[rsgt]

Originally Posted by Freestate

I'm going to piggy off of this thread as I'm having similar issues. I have not started diagnosing the problem but wanted to see if I could get some expert advice as to where I should start.

Issue: When the gas tank is full, the fuel gauge will read just barely over 1/4. As the tank gets empty, it will drop to 1/8. I've never let it get below that before filling. My first thought would be to check the float. Thoughts? Should I check something else first before pulling the float out?

Freestate, Mine was just like yours. Passed 1/4 tank when full then went down as gas was used. Here was the fix: http://67-72chevytrucks.com/vboard/s...d.php?t=744066

[Freestate]

Originally Posted by rsgt

Freestate, Mine was just like yours. Passed 1/4 tank when full then went down as gas was used. Here was the fix: http://67-72chevytrucks.com/vboard/s...d.php?t=744066

Awesome! Thank you for the tip. When I get a chance to do some diagnosing I'll let you know if that was the problem.

[CG]

What a great thread! Just yesterday I hopped in the truck, turned the key, and my gas gauge zoomed way past the full marker. Ill print this out and get to work on it tonight.