2009 Buick LaCrosse - Fuel Level started reading funny. Any ideas?

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As the title states, when my Buick gets below half a tank the needle sticks and stays in one spot. Until I get to around 200-220 miles on a tank. At least it did the first time. I'm approaching 200 now and it's not moving from slightly below half a tank.

I'm wondering if I should try and top end fuel cleaning additive or if the sensor or sending unit needs replaced. It won't be anytime soon as I've already put a bit of money into the car recently after it sat for 3 years and I don't leave town much so I can guess my fill ups accurately.

Thanks in advance.
 
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It sure wouldn't hurt to try a good fuel system cleaner...that's what I'd do.
 
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Any type of fuel cleaner will have zero effect on that issue, and for any other fuel concerns too. IMHO its snake oil.
 
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Take the fuel level sender out and clean the contacts.

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What would you recommend I use to clean the contacts?
It's not the contacts. If there was a problem with the potentiometer and intermittent "opens" or bad sections, the fuel gauge would swing all the way to the full side against the stops when the wiper comes to a bad spot.. You got a float issue or the float arm is sticking.
 
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I replaced my mother’s sending unit in her 20003 less recently. There are videos on YouTube
 

3800Fan

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When I take my car in to have the transmission dipstick tube replaced Monday (can't due it myself due to warranty) I think I'll ask the shop owner about Techron or BG 44k. Lots of people having success with that for this exact same issue and he's a honest and knowledgeable guy who uses additives for some fixes. If he recommends pulling the sending unit I'll put that on my list of to-dos.
 
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The sender is a variable resistor to ground, so you can test it from outside the tank.
 
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When it is sticking, drive it like a bat out of hell, hills/curves/bumps, trying to get more range of motion from the float arm. If that doesn't work, pull the sender and see if it can be cleaned. I mean the traces, wipers, and the float arm pivot point. If not, replace it.
 

3800Fan

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When it is sticking, drive it like a bat out of hell, hills/curves/bumps, trying to get more range of motion from the float arm. If that doesn't work, pull the sender and see if it can be cleaned. I mean the traces, wipers, and the float arm pivot point. If not, replace it.
Can't drive it very aggressively until I replace the control arms. Front bushings are shot.
 
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This fault could be in the instrument panel. I had a Ford Escort years ago. After the car got some age and miles, every so often the fuel gauge would stick on half full, no matter how full or empty the tank actually was. The cause: the wiring connector to the gauge would come loose every once in a while. Pulling out the instrument cluster and snapping the connector back in place would fix the problem for a long time. As a bonus, learning how to pull it all apart made it easy to replace the cluster lamps later as they burned out—typical Ford problem.

Before pulling apart the fuel system, check that gauge first.
 

3800Fan

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This fault could be in the instrument panel. I had a Ford Escort years ago. After the car got some age and miles, every so often the fuel gauge would stick on half full, no matter how full or empty the tank actually was. The cause: the wiring connector to the gauge would come loose every once in a while. Pulling out the instrument cluster and snapping the connector back in place would fix the problem for a long time. As a bonus, learning how to pull it all apart made it easy to replace the cluster lamps later as they burned out—typical Ford problem.

Before pulling apart the fuel system, check that gauge first.
It's since moved to closer to a 1/4 tank. I think the problem is going to be sulfer deposits on the sending unit parts. It had a tank of non ethanol gas in it for 3 years.
 
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Marvel Mystery Oil supposedly contains Stoddard solvent. Running a small bottle in a tank of fuel might help with the deposits. Can't hurt to try that first before wrenching on things.
 

3800Fan

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Well my fuel gauge tricked me. It was fluctuating all over the place or so I thought until I chickened out and stopped for gas thinking I was close to empty. Added some techron and she only took 11.7 gallons out of 17.5 gallon tank.

After my trans rebuild my mileage dropped to 17.5 mpg, now it's at 19.5 mpg. Threw me for a loop.
 
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As the title states, when my Buick gets below half a tank the needle sticks and stays in one spot. Until I get to around 200-220 miles on a tank. At least it did the first time. I'm approaching 200 now and it's not moving from slightly below half a tank.

I'm wondering if I should try and top end fuel cleaning additive or if the sensor or sending unit needs replaced. It won't be anytime soon as I've already put a bit of money into the car recently after it sat for 3 years and I don't leave town much so I can guess my fill ups accurately.

Thanks in advance.
It may well be from sitting so long, this issue was also very common with GM Saab cars. Saab had a TSB that said to first try 20oz of Techron in an low tank then fill it before going into any actual repairs.
I have seen this work well on other vehicles like Chevy Venture, Grand Prix, Buicks, a VW Golf and a few others, some it doesnt help at all. Definitely worth trying before getting any deeper into it.
 
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