Gas Gauge woes (1 Viewer)

[Demonic92]

Hey all,
I have a problem with my gas gauge staying stuck at full after a fill up until some inconsistent amount of time when it finally reads correct. As of now, I have done 195 miles on a tank and it says i still have a full tank of gas. I replaced the sending unit in the gas tank and it solved a different problem I had where the low fuel light wasn't working, but the gauge still gets stuck. Sometimes it's stuck for 30 miles, sometimes it's stuck for 195+ like right now. All I can think of is that it's the gauge itself or some funny electrical mystery. Any thoughts?

 

[jpoole]

It's possible that there is a short and/or bleed over connection causing a false signal to be sent to the gauge. If it sometimes goes back to full after dropping to a good reading, but without you adding gas, then the chance of shorting and bleeding over is higher than a mechanical issue like a sticking float. The short could be anywhere from the sending unit to the gauge but I'd start anywhere you think the wiring could be damaged or may have been messed with in the past.

A mechanical issue with the sending unit or the gauge needle could also be involved. One test may be disconnecting the sending unit signal and/or manually changing the signal (within range of what is normal) while the gauge is on, and high, to see if the gauge drops. That could help rule out a sticky needle. I'm not sure where the needle parks when it has no signal though and that would be important to know. If the needle parks at "full" when disconnected then you may need want to focus your tests for loose/shorting connection vs. current bleed over, etc.

Probably time to break out the multi-meter, manual and pull the sending unit for various tests

 

[manofthewoods]

It's possible that there is a short and/or bleed over connection causing a false signal to be sent to the gauge. If it sometimes goes back to full after dropping to a good reading, but without you adding gas, then the chance of shorting and bleeding over is higher than a mechanical issue like a sticking float. The short could be anywhere from the sending unit to the gauge but I'd start anywhere you think the wiring could be damaged or may have been messed with in the past.

A mechanical issue with the sending unit or the gauge needle could also be involved. One test may be disconnecting the sending unit signal and/or manually changing the signal (within range of what is normal) while the gauge is on, and high, to see if the gauge drops. That could help rule out a sticky needle. I'm not sure where the needle parks when it has no signal though and that would be important to know. If the needle parks at "full" when disconnected then you may need want to focus your tests for loose/shorting connection vs. current bleed over, etc.

Probably time to break out the multi-meter, manual and pull the sending unit for various tests

Good stuff above.
I'm an occum's razor guy (simplest explanation is the most likely)...

A) if you put in a new sending unit and the problem is the exactly the same, then it "has" to be the gauge.
B) or, during the installation the float arm got bent and is hanging up.

Otherwise, old occum's razor doesn't hold up

 

[jpoole]

Good point @manofthewoods . Changing the fuel sending unit included moving connections in that area around and allowed time to inspect them so I would expect that if it was the sending unit or a weak connection on that end that it would have behaved differently after the sending unit change. There are few absolutes in life though so you can't entirely rule out that end of things, but it does make sending unit issues much less likely.

I'd look for the easiest way to simulate the signal for the full range of fuel levels and then test by running those signals to the gauge from the easiest circuit access point. If you test this at the sending unit you are including the entire circuit and the gauge in the test and isolating the sending unit. If you test closer to the gauge you are isolating that end of things. etc. Once you know what the signal range should be and find an easy area to tap into the circuit you may quickly be able find what the problem is (signal, circuit or gauge)...

Occum's razor is a good starting point but from there I'd try the easier things first and run tests that help you isolate parts of the system and zero in on the area where the problem is.

Of course, someone on the forum has probably dealt with this before and may soon chime in with system specs or the common failure points to check, etc.

 

[mudgudgeon]

Could be as simple as a damaged wiring harness.

I had an issue with my old hzj105 where a rock damaged some of the wiring at a have connector under the rear floor. My fuel gauge acted up, then stopped working when the wire broke

 

[Demonic92]

It's possible that there is a short and/or bleed over connection causing a false signal to be sent to the gauge. If it sometimes goes back to full after dropping to a good reading, but without you adding gas, then the chance of shorting and bleeding over is higher than a mechanical issue like a sticking float. The short could be anywhere from the sending unit to the gauge but I'd start anywhere you think the wiring could be damaged or may have been messed with in the past.

A mechanical issue with the sending unit or the gauge needle could also be involved. One test may be disconnecting the sending unit signal and/or manually changing the signal (within range of what is normal) while the gauge is on, and high, to see if the gauge drops. That could help rule out a sticky needle. I'm not sure where the needle parks when it has no signal though and that would be important to know. If the needle parks at "full" when disconnected then you may need want to focus your tests for loose/shorting connection vs. current bleed over, etc.

Probably time to break out the multi-meter, manual and pull the sending unit for various tests

I'm not sure if it's electrical because I would expect more of an intermittent issue that way.

When i fill up, the gauge needle gets stuck at full for any amount of miles. Once it decides to drop down, it continues going down normally and reads accurately until i do a full fill up again, at which point it is then stuck at Full. It almost makes me think that the gauge just gets stuck once it's at full and it takes just the right road bump to drop it down.... that might be crazy though.

Last time it was stuck at full until 200 miles at which point it dropped to 1/4 tank, and this time it was stuck at full until 140 miles at which point it dropped to 1/2 tank.

There has been a couple of times that the gas gauge got "un-stuck" pretty early into a full fill up, but once i drove up a hill which caused the gauge to read higher than normal (because of fuel slosh, etc.) it gets stuck there again after the hill.

 

[robnicko]

Good stuff above.
I'm an occum's razor guy (simplest explanation is the most likely)...

A) if you put in a new sending unit and the problem is the exactly the same, then it "has" to be the gauge.
B) or, during the installation the float arm got bent and is hanging up.

Otherwise, old occum's razor doesn't hold up

i had to google Occums razor !

 

[Demonic92]

Funny update. Did 500+ miles of driving today, all highway. I believe because there was no city driving behavior and rough road conditions that come with the city, the gas gauge did not drop at all after a fill up, two times. I only knew when to start worrying when the light came on... when the needle showed full. So the sender is definitely working!

 

[manofthewoods]

Funny update. Did 500+ miles of driving today, all highway. I believe because there was no city driving behavior and rough road conditions that come with the city, the gas gauge did not drop at all after a fill up, two times. I only knew when to start worrying when the light came on... when the needle showed full. So the sender is definitely working!

View attachment 3401545

well...
not necessarily. The circuit for the light is different than the circuit for the sending of the fuel level. It would/could be very possible that the float is stuck at a "full" level. Of course, it could be the gauge, etc.

Please keep us posted as to what finally fixes the situation. And...

Good luck

 

[Demonic92]

Damn it!!!!!!!!

 

[Rifleman]

Funny update. Did 500+ miles of driving today, all highway. I believe because there was no city driving behavior and rough road conditions that come with the city, the gas gauge did not drop at all after a fill up, two times. I only knew when to start worrying when the light came on... when the needle showed full. So the sender is definitely working!

View attachment 3401545

Now that's odd, my gas gauge never wants to stay at full even after after a fill up, and after about 40 miles of driving it seems to want to race to empty
Then at 150 miles it's just a tick above empty and stays there until the low fuel light come on

 

[Brindleboxer]

What happens if you only fill to approximately 3/4 tank? Does the gauge still go to full and exhibit the same issues?

 

[manofthewoods]

What happens if you only fill to approximately 3/4 tank? Does the gauge still go to full and exhibit the same issues?

Excellent suggestion. If it does stay stuck at 3/4 then I'm voting for the float arm rubbing/sticking on something.

If not

 

[Demonic92]

Excellent suggestion. If it does stay stuck at 3/4 then I'm voting for the float arm rubbing/sticking on something.

If not

I don't know when the next time i'll be able to test that will be. It's been stuck at full for the last 800 miles.

While i'm here, i just finished driving about 350 miles in 90+ degree heat. I could smell fuel when i parked and stopped the engine. I unscrewed the fuel cap and had to let vapors out for like 15 seconds before taking it fully off, and then i stuck my key in the fuel hole and let more out, making my hand damp in the process. Is this normal? Only happens in the very hot weather i think. Where is it supposed to vent? Or is it?

 

[Rifleman]

While i'm here, i just finished driving about 350 miles in 90+ degree heat. I could smell fuel when i parked and stopped the engine. I unscrewed the fuel cap and had to let vapors out for like 15 seconds before taking it fully off, and then i stuck my key in the fuel hole and let more out, making my hand damp in the process. Is this normal? Only happens in the very hot weather i think. Where is it supposed to vent? Or is it?

This is a known issue with the fuel evap system, do a search on how to replace your charcoal canister
Replacing your Charcoal canister should take care of the gas tank being pressurized

 

[Demonic92]

This is a known issue with the fuel evap system, do a search on how to replace your charcoal canister
Replacing your Charcoal canister should take care of the gas tank being pressurized

Damn. It's always something. Thankfully seems easy enough. Thanks

 

[rhc404]

Damn. It's always something. Thankfully seems easy enough. Thanks

I've been chasing this issue too and the charcoal canister didn't fix it. There are a few threads on it but the conclusion is that it's an issue with the ethanol blended into modern gasoline lowering the boiling point, and the 90's era EVAP system can't keep up. It's only an issue for me after big elevation changes. Part of the exhaust also runs near a corner of the tank and it may be contributing if the truck spends a lot of time idling or at crawling speeds.