sirwill

This all started about a month ago right after I filled the gas tank. It occurs every time I get gas now. After I fill the tank, when i turn the car back on, I get an immediate 3 or 4 dings for the gas gauge. it is pegged on empty with the light on. Then after a short while of driving it will slowly go up to about an 1/8th of a tank, and then go back down to E and ding again. It will do this a few times, then goes up to about 1/2 tank, and then down to E. This behavior happens for the first 2 or 3 times I drive it, or about 15-20 miles. Then it behaves very normal until I fill up the tank again. I go through this every time I fill up. Gas cap appears fine. No check engine light.

The first time it happened I freaked a little bit, pulled over, and checked the gas cap. I noticed that when I took the cap off I could see down the gas tank neck. I thought there was a little metal flap or door there before, but there isn't one now. Is it supposed to have a flap there? Could this be the problem or is there some other problem? I think I am about 4k miles out of warranty.

Any help would be appreciated.

CemStone

Same thing happened to me on my 06 Trailblazer SS, took it to the dealer, replaced fuel regulator sensor. Problem Fixed

sirwill

Do you know a part number? I haven't found a part named that as of yet. How much did they charge you to fix this?

rbarrios

I doubt its related to the little metal flap that has fallen off the filler neck.
This will mostl likely be one of 2 things....
A bad fuel level sender..
or
Sulfur buildup on the fuel level sender.
the 1st- if it is bad will require the dropping of the gas tank (its recommended you drive until youre very low on gas to make dropping easier). but they will most likely replace the entire fuel pump and level sender/sensor- as theyre sold as 1 piece. I think Ive read some guys replace the sender only.
the 2nd is easier to fix......
sulfur builds up in the level sender and causes bad readings.

rbarrios

the fuel level sender- has a small float that moves according to the level of fuel. this float moves a small mechanism over a varistor. a variable resistor. which sends a signal to the dash cluster- and thats how you get your fuel level...
well, when you get the sulfur buildup- the mechanism cant read the correct resistance on the varistor... and you get that erratic fuel level.
IF it is excessive sulfur you can hopefully correct this.
Go to auto parts- buy a bottle (preferrably 2) of Chevrons TECHRON fuel system cleaner. they sell 2 sizes- treatmentfor 12 and 20 gallons. whichever you get- make sure you dont dilute it too much by putting in too much gas.
But make sure the bottle says something like "HELPS CLEAN SULFUR BUILD UP- that causes erratic fuel gauge operation"
after your 2 bottles- hopefully it has corrected your situation.
Ive seen several Trailblazer owners report that the techron helped and the gauge worked again... AND Ive seen some whose fuel level sender was now bad and had to have it replaced....
IF the repair facility does replace the entire fuel pump+ sender- youre looking at- at least $300 +.. since the fuel pump itself is in this price range.... then figure labor.....
try the techron.... its also great for cleaning the fuel injectors...

Jackals7

I have an 05 and had the same problem. It was the fuel level sensor located inside the gas tank. The part was around $140.00. Dealership wanted $400 for parts and labor. I did the repair myself. Just take your time and get as much info as you can about removing the gas tank. Be sure to label everything as well.