The Stovebolt Site Forums The Shop Area The Electrical Bay Gas gauge goes straight to full

Hi guys, my gas gauge goes to full and stays there until ignition is turned off. 1947 using new classic part gauge. The needle goes back to E when ignition is turned off. Have the sender going to F side I am mostly sure, ran a ground from a screw that screws into the tank on the sender to frame. Any ideals

Full on the gauge is the default for no current, maximum resistance. My guess would be you have an open circuit.

Thanks for the reply, Iwill check it out furhter. Let's hope it's not on top of the tank!!!

Full with ignition on, means one of two possibilities in my experience. The tank is full. Or you do not have a good ground between top of sender and the negative battery post (through the cab, through the frame, through the battery strap/cable on the way to the battery post).
Carl

Here is a site that was sent to me regarding the fuel gauge:

https://www.fillingstation.com/articles/fuelgaugetesting.htm

If it's going to full, you at least know your gauge works. The above site should help you with some testing.

I'm having problems with my 50's Chevy 3100, got the sending unit from classicparts and hooked positive to post of unit and ground to a bolt that mounts the unit to the tank.
The gauge read E when key is on though.

fat47,

Your sender/system is most likely not grounded.

Run a "test" ground wire from a sender mounting bolt/screw-stud to a good ground (using another wire for a sure ground).

You say that you have a "ground to a bolt that mounts the unit to the tank." What is the other end of that ground wire bolted to? It needs to be attached to bare metal which is a part of the grounded chassis (frame). I will bet 12 doughnuts of various flavors that is your trouble.
Carl

I honestly couldn't find where the gauges in the dash are grounded at (if they even are?) and I assume the fuel sending unit is grounded to frame but I'll have to check tomorrow try testing what Tim suggested.

You can run into a gauge cluster grounding issue with a restoration it the new paint insulates it from the dash. I would run a ground wire from the top of the sending unit to a good bare metal part of the chassis first.
Carl

50ChevyGuy,

I do not know which gauges might have to be grounded by way of the gauge housing, but the lights would be grounded through the gauge housing (if the gauge lights go on, the housing is grounded).

Use the same diagnostic for this (as I recommended for the sender that resides in the fuel tank).

For the gauge housing: turn on the lights; then, run a grounded-wire from any clean-metal spot on the gauge housing to a body ground. Do this by hand - you will not get shocked if you hold the insulation on the wire.

A good spot to hold the wire onto the gauge housing would be against a bulb housing (that is where they make their ground). Run the other end to the ground terminal on the battery.

Found the ground for the sending unit and it probably needs redoing, so I hooked up a test wire as a new ground and ran it to a good ground that I have.
It didn't change anything and the needle just stays at E.

50Chevyguy,

I apologize for misleading you. My recommendation to check the ground wire was in response to the original post. A "pegged to Full" gauge is often a bad ground at the sender.

I read your post too quickly and assumed it was the same symptom as the original post.

Did you ground the gauge-housing to see if the instrument lights work?

As far as you getting no reading: it could be a bad gauge, a bad sender, or a break in the lead from the gauge to the sender.

Do you have the power lead going into the correct side of the gauge (the "E" empty side of the gauge, I think?

You lost me.
You originally stated that with the key on, the gauge goes to full.
Now, with a good ground, "It didn't change anything and the needle just stays at E."
Since it no longer goes to full with the key on, is that not a "change"?
If it reads E with the key on, either the tank is empty or nearly so, or you have a bad sending unit.
Carl

I have the same problem with my new sending unit,(from L.M.C.)When I first installed it,no problems. then I installed a new wiring harness. Turned on the key-FULL. I had less than 1/2 a tank. I checked the continuity at the gauge itself. Gauge is fine. I checked my ground connection at the sender,and that,too checked out fine. The problem is with the sending unit.It won't register with everything connected,)KEY ON),and moving the float! Even though they are new,doesn't mean they work O.K. Even though I have less than 1,000 miles on the truck since i bought it,there's no warranty,since I bought it 3 years ago. I'll just have to buy another one,and HOPE!!

I have a brand new sending unit and when the ignition is on the needles jumps to E. So I assume it is getting power, and I ran a test ground to check if that was the problem and still the needle staying at E.
With the ignition off, the needle drops like should. Really hoping its not the gauge itself but the wires between sending unit and gauge.

Did it originally go to F with the ignition on, as your first post reads? Did the good ground fix solve that issue?
Here is my stupid question. How much gas is in the tank?
Hang in there Man, we're gonna get this figured out. We just have to go about it systematically.

First was this a 6 volt or 12 volt system? Is the gage a 6 volt gauge? If it is you need a resistor in line on the gauge if you have 6 volt gauge on a 12 volt system. If you connected the hot to the wrong side of the gauge you most likely will need a new sending unit. Just some thoughts. Keep us posted.

- 6v system, gauges are still original
- Gauge needle jumps to E from below E when ignition is turned on, then doesn't move from there
- brand new sending unit from LMC Truck
- tested new ground, didn't work
- has at least half of a tank so should read something at least..

If you have a meter test your sender


If you have 1/2 a tank is should read about 15 ohm

...test...

52Carl has it right. You will find once you get a good ground on the gauge, it will work as designed. Without it, all you are doing is sending full power straight to the gauge, causing it to jump straight to F. Had the same issue on my 1st truck back in the late 70's, of course I was only 15 at the time and pretty darn proud of having a "F"ull tank of gas! A week later I still had a full tank ;(

When you say, "Gauge needle jumps to E", where does it jump from before it ends up at E?
Your description confuses me when the very next words are, "doesn't move."
I don't understand how something can jump somewhere, and not move, at the same time.
Carl

My apologies, I left out parts and edited the post.

The gauge needle sits below E when ignition is off, then when ignition is on it jumps up to E then remains there.

-Tested the sending unit and it operates properly
-Check to verify and the truck does have around 1/2 tank of fuel in it

Next I'm going to replace the existing wires to see if that is the fix, then if that doesn't work then I have to assume the gauge itself is broken.

I had a problem with a new sending unit where the float hit the side of the tank and wouldn't read right on the gauge. It would function perfectly as I moved the float up and down while it was out of the tank.

Fixed! Swapped out the old wires for some new ones and worked!
Thanks everyone for the advice and assistance!

Shane, thanks for closing this one out. This was an interesting thread with some good foundational troubleshooting guidance. Just one final question, exactly what wires did you finally replace?

I replaced the wire from the sending unit to the gauge itself, which of course was the last thing I suspected and checked.

I removed the sending unit from the tank and tested its movement with new temporary wires, testing first the ground then the (sending unit -> gauge) and replacing that wire fixed the problem.