15mpg??????
 

2004gl2 3400.
i gave a full tuneup, kandn air, tried running 93 and yes new fuel filter and fuel injector cleaner. i am still only getting 15mpg cant be normal. ive been in 2 aleros and one grand am with 3.4v6 none had gas mileage this bad there has to be something wrong. no gas leaks,car runs mint. what can be wrong what do i do?? i ran this test 3 times to be sure it was accuate.

Its been told that higher octane gasoline is not as fuel efficient.

have you tried staying out of the accelerator a little bit more? Maybe you have a loose connection somewhere in your airbox. Could be your exhaust it clogged up...could just be a leak in your fuel system.

Mines terrible to, and i ahve a 2.4! 18mpg driving as eassssy as i can!

Plug a good scanner into your data link port and get real time O2 readings from your sensors I would be willing to bet its time to replace them, clean the the air filter and spray your Mass Air flow sensor off.

I would do 55mph if I cared, but I don't so I keep it at 65 on the highway, and below 45 in city. I think you need to back down on the speed there buddy...I seriously doubt that you are that much of a law abidding citizen, and if all else fails join sams club can't beat there gas prices around here. They are always cheaper then the big boys.

one of my airbox screws is stripped but the other one stays down pretty tight? its not lose though? how do i clean the maf? so try replacing both 02 sensors? car has 50k on it so im sure it wouldnt hurt to change em out. is there anything electronically that could be wrong like egr valve or computer system? no ses lights on and car runs good.