i have a 94 z28 pretty much stock w/ magnaflow cb and k&n and i have only got 12-13 mpg ever since i got it and over that time i have changed bad o2 sensors, cleaned MAF, changed fuel filter but it still really hasnt changed at all, HELP!!

 

bump, and it is a 6 speed

 

Ryan's Guide to MPG

Just making a general list, pick and choose what you have or have not done and go from there.

Plugs
Wires
Cap & Rotor
Clean Air Filter (I see you have a CAI, they can be washed depending on brand)
Fuel Filter
O2's
Check for low tire pressure
Clean MAF
Change Oil (As oil is broken down through driving it will slowly eat away at your fuel economy, as does thicker oils)
Check for Exhaust Leaks
Driver mod

If I remember anything else I'll add it.

 

i actually do have a small exhaust leak i hear while the cars running and dont really beat on it often. But i did get some champion plugs not too long ago and some wires so i got those. The only thing i havent replaced is the cap and rotor, do you think i should? .... do you think an exhaust leak would take off 2-3 mpg? and the car runs great

 

man I have the hotcam kit and drive a lil fast from time to time and my gasmilage is usually a little better than that. check your injectors. Another hting not listed, that seems to make a few more miles into the tank is a PCV Valve. Didnt see anyone mention that.

 

Bingo.

An exhaust leak will lead to an incorrect lean reading on the o2's. The PCM will compensate by dumping fuel at the problem. Also possible false knock retard won't help your fuel economy either.

 

alright thanks for the replies, i knew the exhaust leak was one of the reasons... how do i know if the injectors are bad? and ill look into the pcv valve and the knock retard

 

You still havent said what kind of driving you are doing and how hard you are driving it to get that gas millage.

 

i drive 3000 rpms or less when i drive regular then i prolly get on it about once or twice a tank.... idk but today my car started running like **** and rattles at idle and feels like lost power, when i rev it sounds fine and revs normal but drivin is rough and feels like a huge exhaust leak, can someone help!??

 

Sounds like not only an exhaust leak but a vaccuum leak as well.
Doug

 

huh, that sucks, i beat the **** out of my cc306 cammed car with mixed stop/go and hw and got 19.5 mpg with it :-)