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Discussion Starter · #1 ·
2014 GC Overland 3.6L with 53k miles

Fuel gauge has worked fine since I purchased this GC in early Dec 2018. Filled up on Sunday, and ever since then, fuel gauge is stuck on full even though I've driven it daily. Trip meters and fuel mileage appear to be accurate, and gauge should be currently reading between 1/2 and 3/4 tank. Didn't find anything via forum search, now searching more broadly online.

Will try the obvious items first: fuse, test fuel gauge sending unit for voltage & resistance.

If you experienced this, what was the solution so I can start narrowing it down?
 

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I haven't experienced this but would check for a stuck float in the fuel tank. Couldn't hurt to add a concentrated dose of fuel injection cleaner. It's also possible condensation in the tank has caused the float mechanism to corrode and subsequently get stuck when it was filled to full.
 

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Trip meter doesn't use info from the gas gauge at all. The mpg counter doesn't either, but I could be wrong on that, I "think" the mileage counter just extrapolates mileage based on the fuel injection information from the PCM.

Ethanol can leave a white chalky residue behind, perhaps that might be gumming up the float in the tank....

Like mancerator suggests, a good fuel cleaner added to the tank might help. One that advertises its for correcting the problems from ethanol. Chevron Techron is pretty much thought of as the best cleaner on the market, although I have to admit that seems to be based on opinion as far as I can tell. I use it though.....

Give the gas tank a good rap from the bottom several times on the drivers side, that might unstick the float.

If you have the information, you could pull the connector and check resistance at the right pins for the fuel level, see if its in the range for a full tank or partial tank....

Look for shorts in the wiring....

As I "understand it", meaning I don't really know, I'm guess from what little I do know about the tank and floats....
...the WK2 has 4 floats for fuel level in it... ....2 on the fuel pump and 2 on the auxiliary pump/pick-up on the other side of the hump.... ....the 2nd set of floats are obvious, to measure the fuel level on that side of the hump after the fuel level goes down enough to divide the tank into two tanks on either side of the hump.... ...I suspect the 2nd float on each side is for the low fuel level....

What are the chances that all four floats are stuck at the same time? And if I understand how the other 3 floats work, which I might not understand it right, they won't start to drop till your pretty low on fuel .....

...so if you get you get the fuel gauge to drop almost to 3/4 when your nearly out of gas, and the low fuel light turns on, that might be a good indication that its just the main float that is stuck.....
 

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Trip meter doesn't use info from the gas gauge at all. The mpg counter doesn't either, but I could be wrong on that, I "think" the mileage counter just extrapolates mileage based on the fuel injection information from the PCM.

Ethanol can leave a white chalky residue behind, perhaps that might be gumming up the float in the tank....

Like mancerator suggests, a good fuel cleaner added to the tank might help. One that advertises its for correcting the problems from ethanol. Chevron Techron is pretty much thought of as the best cleaner on the market, although I have to admit that seems to be based on opinion as far as I can tell. I use it though.....

Give the gas tank a good rap from the bottom several times on the drivers side, that might unstick the float.

If you have the information, you could pull the connector and check resistance at the right pins for the fuel level, see if its in the range for a full tank or partial tank....

Look for shorts in the wiring....

As I "understand it", meaning I don't really know, I'm guess from what little I do know about the tank and floats....
...the WK2 has 4 floats for fuel level in it... ....2 on the fuel pump and 2 on the auxiliary pump/pick-up on the other side of the hump.... ....the 2nd set of floats are obvious, to measure the fuel level on that side of the hump after the fuel level goes down enough to divide the tank into two tanks on either side of the hump.... ...I suspect the 2nd float on each side is for the low fuel level....

What are the chances that all four floats are stuck at the same time? And if I understand how the other 3 floats work, which I might not understand it right, they won't start to drop till your pretty low on fuel .....

...so if you get you get the fuel gauge to drop almost to 3/4 when your nearly out of gas, and the low fuel light turns on, that might be a good indication that its just the main float that is stuck.....
Good information Mongo. I do notice the remaining driving distance indicator must somehow be monitoring fuel level as mine continues to adjust based on the current MPG I'm getting and always goes to somewhere just under 400 miles when I fill up (2014 V8). If that's true and the main float is indeed stuck, it would seem JeepCG001's driving distance should be hovering around 400 even though he has less than a full tank. If that number has fallen as he used fuel, maybe the fuel gauge in the dash isn't working right. Pound on the dash above the gas gauge? :)
 

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Yea, DTE, Distance till Empty does seem to monitor fuel level and calculate off the latest mileage at the moment. I can't imagine how you do it otherwise....

The MPG, I "think" a lot of people assume its being down like they do it in their head or with pen and paper, they divide the miles driven by how much fuel has been used from the tank. So they assume the MPG display on the car is doing the same thing and uses the gas gauge.... ....I don't think so, the PCM is constantly setting a fuel injector pulse width that determines the exact amount of fuel being injected in the engine, simply math with the rpm at the moment would tell the fuel consumption, with the speed, you have an instant MPG derived just with engine and speed info, no need to track gas gauge and miles driven. So the MPG display wouldn't be effected by a stuck gas gauge. The average MPG is just averaging the samples of the instant MPG.... ....I could be wrong, but that certainly seems to be the way it works....
 

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Agreed. The "range" display only needs to know how many gallons are available multiplied by the calculated average MPG. The fuel gauge is already measuring remaining gallons so theoretically the "gallons" component for "range" calculation could come off the same float as the fuel gauge. If that float is stuck and is telling the gauge the tank is full it should also be telling the "range" indicator the tank is full. Theoretically of course but it doesn't make sense to have a second fuel float just to calculate range.
 

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Discussion Starter · #7 · (Edited)
Thanks everyone, and I definitely know the trip meters and fuel mileage are unrelated to the fuel gauge. Only made that comment because its's how I'm tracking data to avoid running out of gas, LOL! Current plan is to try bumping the tank to see if it breaks loose and also add a few bottles of a good FI cleaner (can't hurt anyway).
 

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Agreed. The "range" display only needs to know how many gallons are available multiplied by the calculated average MPG. The fuel gauge is already measuring remaining gallons so theoretically the "gallons" component for "range" calculation could come off the same float as the fuel gauge. If that float is stuck and is telling the gauge the tank is full it should also be telling the "range" indicator the tank is full. Theoretically of course but it doesn't make sense to have a second fuel float just to calculate range.
Yea, a 2nd set of floats on each side of the tank is puzzling. I was guessing for low fuel lights, make them independent so they don't fail if the gas gauge fails.... ...but just like the range calculations the low fuel can come from the main floats....

Something just occurred to me, I've been assuming there must be some sort of ball floats in the pick-ups of the pump and auxiliary pick-up on the other side, you need some way to close the pick up on one side if it runs out of gas before the otherside, otherwise you'd suck air into the fuel pump.... ...could the 2nd set of floats be for opening/closing the pick-ups so the pump doesn't suck air?
 

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Discussion Starter · #10 ·
Update: I added 2 bottles of Techron this morning to what should be about 1/2 tank. On my drive home, the needle appears to have moved for the first time since Sunday when I filled up. It moved from full to about 15/16ths (in between 7/8ths and full). Wondering if one float is stuck, or stuck worse than the other, and this is the average reading between the two. Need to investigate further this weekend...
 

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The Chevron Techron is good stuff.... ....be patient, you can't expect it to remove any gunk or coating in a matter of minutes, it will take some time....

The float might not even be stuck, the float runs a contact over a boards with variable resistance, thus changing the resistance of the sender as the float goes up and down.... ...the ethanol in the gas leaving behind the white chalky coating can cover the contacts, so you put something in to start dissolving it, it starts making a connection with some points on the board, but not all and you get a partial reading...

...keep in mind, the 2nd float on the auxiliary pick-up, probably only goes as high as the hump in the tank, the float on the fuel pump will measure level for the entire tank minus the level on the auxiliary pick-up below the hump, so the auxiliary pick-up side adds to the level the main float reads....

Think about it, if the auxiliary read the fuel level all the way to the top of the tank, then you would be reading the same fuel level twice, it wouldn't be accurate.... ...that's my guess, you never know, maybe both floats go from top to bottom and they wire it or a computer simply halves the readings and adds them....
 

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Discussion Starter · #12 ·
If I need to gain access to the sending unit (e.g. to test resistance), where is it located (e..g under the back seat, under the back cargo area)? And is there a "door" like the Cherokee has? Found lots if info online, but haven't yet found how to access the WK2 sending unit.
 

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I just looked at some parts pictures of the WK2 Fuel Tank, Fuel Pump and Auxiliary Pick-Up.......

Umm, it appears I've made some assumptions that are not true.....

There is no 2nd set of floats on the pump and auxiliary pick-up, they each have one float each....
...every photo of the parts I can find, has a single float.... ...just the OEM Parts Catalog has drawings of the parts, and the drawing shows the floats in both the min and max position, that leads you to believe it has two floats.... ...nope just one float per item...

btw, you can clearly see the contact board that the float rod slides a contact across the board to change resistance, in the photos.... ...this is what gets coated from residue left behind by ethanol and additives in the fuel....

Now the fuel tank, the hump in the center for the driveshaft and exhaust, that hump goes up to what appears to be 90% the height of the tank, not halfway like I had assumed....

So this means, its very much two fuel tanks just connected by a small channel at the top.... ....so when you fill the tank, you really fill the drivers side and the fuel then spills over into the passenger side to fill until you fill the tank...

So, yes, the auxiliary pick-up float does go all the way to top and the gas gauge must just be summing the readout of the sensors, or in term of the electrical wiring they could simply be wired so that the gauge is at max for both sensors at max level and the gauge on min when both sensors are min level, anywhere in between reflects the true level, just like if it was a uniform single tank with a single sensor....

There has to be some sort of shut-off or capping of the pick-up for if one side runs dry before the other, else you'd be sucking air with fuel into the pump.... ...I would think the simplest setup would just be to draw from both sides at the same time and have some sort of valve that has be immersed in fuel to be open, thus shut when one side runs dry so as to just draw from the side still with fuel... ....its not hard to imagine scenarios that one side will have a higher level than the other... ...so assuming both sides level would drop in sync and no sorta of shut-off would be needed is just asking for the engine stalling from fuel starvation while there is still fuel in the tank....
 

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If I need to gain access to the sending unit (e.g. to test resistance), where is it located (e..g under the back seat, under the back cargo area)? And is there a "door" like the Cherokee has? Found lots if info online, but haven't yet found how to access the WK2 sending unit.
The connector at the very top of the fuel pump and auxiliary pick-up, which judging from the photos of the tank, you'd need to lower the tank to get access to it...
If you had a wiring diagram/connector pinouts, you could disconnect the right connector in the harness and test the right pins in the connector.....
 

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Discussion Starter · #15 ·
What a PITA. Looks like the exhaust may have to be dropped to get the tank low enough to access the wiring for the sending units.

Gauge now reads 7/8 tank, so it's moved a little, but should show just under 1/2 tank right now based on how much I've driven. Applied some rubber mallet influence below where the pumps and sending units appear to be located, will see in the morning if that changes anything.
 

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I'd buy 2 more bottles of Chevron Techron and add it to the tank before I'd start messing with dropping the tank. Likely you need to remove the driveshaft as well as the exhaust to lower the tank. You did read the instructions on the bottle that says its enough for 15 gallons of gas, meaning you need to add two bottle for a full tank, well almost 2 full bottles, for something like your problem, I'd lean on the heavier concentration.... ...I haven't seen the larger bottle for 23 gallons of gas on store shelves for years, perhaps you found the larger bottle, but if not use two bottle per tank full of gas...

Keep in mind the pivot point and sensor are halfway up the level of the tank, so if your at 1/2 a tank or less, the fuel level with cleaner is below the pivot point, thus not dissolving the residue anymore....
 

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Discussion Starter · #17 ·
Oh trust me, I'm trying other things before dropping the tank, just venting about what it will take if I have to go that route. I bought 2 bottles that treat up to 15 gallons for a higher concentration, but it may not be enough. Will probably add 3+ bottles after I fill up next because I know the sending unit pivot point is mid-tank level. Hopefully this fixes it, but I'm not highly confident yet...
 

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Just throwing it out there .......
If the range is showing some info, then it may be reading the tank sensor. The problem may be related to the fuel gauge. Check to see if the needle is moving without restriction.
 

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Discussion Starter · #19 · (Edited)
Gauge moved a little more over the past few days, so float is therefore moving, but gauge is still inaccurate. Seems to be residue on the sending unit resistor that's affecting signal integrity. Float may or may not have been truly stuck the first week after filling up, no way to tell that now, and doesn't matter at this point. Planning to add a heavy dose of Techron fuel system cleaner, fill up, then let it sit for a while before driving.
 
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