i recently changed out 2 brand new walker o2 sensors (front 2 on ypipe)....new air filter.....fuel filter....ngk coppers.....cleaned TB...and new KS....

after changing out the o2's im still gettin the same gas mileage as i was gettin b4 changing out the o2's.....i dont understand what is goin on...seems like i have done almost everhything but i am still gettin crappy gas mileage....does anyone kno what i can do to make it better?

also i have noticed that my car really smells like exhaust/gas during early start up....i have 100k miles and i was wondering if this is caused by my cat? will replacing the cat somehow increase my gas mileage?

i get about 300 miles on a whole tank with all highway driving.....

 

I'd be curious to find out what your issue is too. I have a 98SE 5-spd of which I'm the original owner. Besides the 60k service at 54k, I've never done anything but oil changes and cleaning/reoiling K&N. The car still gets 26-28 highway. I know someone who has a 96 GXE with over 140k, which was purchased used at 45k, and he says he has never serviced the car at Nissan and the mileage is at least 25 hwy. So I've decided to bypass the next 60k service unless my mileage dips.

I just drove 341 miles and put 15.6 gal in, city/hwy combined. It's the same every time, around 21.x mpg commuting, my gas mileage is like a Rolex or Omega watch.

 

try increasing your tire pressure. i did and i got a noticable difference, the only downside is that the ride is a little bit more bumpy. i also dont let the rpms get over 3500.
good luck