Fuel gauge is bouncing all over the place - 2006 Chevrolet Trailblazer

Just replaced fuel pump and fuel indicator sensor on my Bonny and fixed the problem,this seems to be a very common problems with this car

usually this is caused by gas moving around in gas tank and causing float to move around which is what controls the gauge reading. Some have a cove around them to prevent this. Alot of times when someone has the fuel pump replaced they have this problem because float was either bent or not placed in tank properly. hope this helps

this is caused by only one thing, and that is the gas gauge sending unit inside the gas tank, replace it.

There are only two possibilities. The fuel sending unit in the tank, or the dash mounted gage unit.
I suspect the fuel sender.

could be faulty gauge or sending unit in the tank. if you can get ahold of a scan tool, see if the fuel lvel reading on the scan tool agrees with the gauge. if it does than you have a faulty sending unit.if it does not than you may have a faulty gauge.

See if your leaking any gas by placing a box underneath the car, second your fuel float may be going inside the tank and or it could be a fuel pump or sending unit issue.
Call a junk yard or salvage place if you find you need parts..

I had previously replaced the failing fuel pump on my '98 K2500 when it went out entirely. I was ready to replace my 2000 K3500's fuel gauge as it was acting up.
When I started the engine, the gauge would bounce from the middle to way past full then back. It would also jump sporadically while driving on level ground.
I checked the electrical connections at the tank and made sure the frame ground strap located nearby was making good contact. Nothing changed until I removed the instrument panel and cleaned the connections on the back. The fuel gauge seems to be operating correctly now.
There are videos on YouTube that show how to remove the instrument cluster if in doubt. Mine dash has a pop-in plastic bezel followed by 4 screws to hold the cluster in place. It took about a half hour to inspect & clean the dash connection vs. $250 to replace the pump/sending unit combo. Hope this helps.

gauge itself failing (dash) rheostat part behind needle worn

gauge failing (dash)

The bouncing is cuased by a fault fuel sending unit located in the gas tank. Sometimes you can change just the sender but you'll probably have to get it from your local dealership. Most parts stores will sell the sender only with the fuel pump and it can cost serveral hundred dollars. Either way you have to remove the gas tank to change it. Your gas milage problem can be cuased by a a bad fuel pressure regulator which are known to go bad on those cars.