Hello, just signed up to this forum. I went trough about 40 pages of threads, didn't see anything similar to my problem. The car is a 1996 Olds LSS, 3.8 non supercharged, which i purchased last October. The gas mileage is terrrible, about 16 mpg average. Did all the basic tune-up stuff, gained a 1 mpg. Also, no check engine light. Just wondering if anybody might have a rough idea, what the problem could be. Thanks.

Well for me that'* kinda average and brand new e.p.a. estimate was 17c/23h. I would like to say your at normal mpg but I am not a expert like Dan, Bill, Venom ect. But I'm pretty sure thats normal.

Did you replace the O2 sensor? Also winter blend fuel kills mileage.

thats not normal, my wife gets 25 to 28 and she drives like john force. what exactly did you replace?

Thanks for the responses so far, plugs, wires, air filter, is what i changed so far. The reason behind the question, was that i owned a 1995 Olds Regency Elite, before this car, I would average 25-30 mpg with that car, and straight highway, upper 30'*. So i am a little disapointed in the mileage i am getting. Thanks..

try fuel filter, then you might have to get into O2 like danthurs says

Ok, thanks, I will try a fuel first. And, i thought a bad O2 sensor, would throw a check engine light on?

it may or may not, on the way to being bad could be less accurate.

What 02 sensor would have an effect on fuel mileage?
The one in exhaust manifold or the one by the cat converter?

the downstream one just checks the converter

that reminds me, your cat could be starting to clog.