Ive realized lately ive been getting terrible gas milage.... mostly normal driving shifting anywhere from 2.5 to 3.5 rmps a good ammount of highway driving.
Last tank of gas i got 100 miles to the tank...... could this be from misfires?

 

bad front o2 sensor

 

Do you have a wideband? What AFR are you getting during cruise? Can you log STFT and o2 feedback with evoscan?

 

wow dude, that's really bad. this just began recently? you haven't changed anything on the car that would cause that? did you do a search for a fuel leak maybe? if you're misfiring, a tune might help, but 100 miles a tank is way low.

 

re-tune, bad o2, clean your MAF, check injectors, check for boost leaks, use SEAFOAM!

 

well how r u drivin it cruising driving? or getting on it all the time? Any check engine light codes, blinking check engine light?? Id say if its running like that, first place would be a boost leak test, if theres no check engine light. Next whens the last time you changed your spark plugs??, if a while couldnt hurt to change em, and put in a bottle of some lucas fuel system cleaner... that would be the best bet, unless a cel code is on in which case could be the culprit of your bad gas mileage.

 

A few months back I was getting a very slight missfire once in a while and it felt way down on power also.I was getting maybe half of my normal MPG, anyways I just let it do it for a while then thought I would just change my plugs.Changed those suckers and felt like an idiot for burning through $200 in gas in 2 weeks because I needed a set of $10 plugs...might just want to check on them.my missfire didn't even sound bad either.

 

yea about the same time this has been happening im getting some knock... SES light flickers when i make boost im thinking either misfires or a boostleak?

 

also ive changed my spark plugs about a month ago... maybe its the way i gapped them? i went according to the manual with the correct gap

 

Bad front O2, had the same problem.

 

02 sensor (front). im on sensor numero 3 (little b@stards). PITA not cheap, but same symptoms. idles like crap, running rich (black smoke), horrrrrrible mpg. evo scan that guy and replace the sensor. plugs will not cause that, only misfire issues. pull the code and post up.

 

black smoke means your running rich, so theres a possibility your plugs could be fouled, what kinda plugs and what did you gap them at? A blinking cel is caused by misfire. What boost are you running, typically if its higher then stock boost levels, you wanna gap the plugs down to anywhere from .020-.024. Best bet is to run some fuel system cleaner in the tank when it goes to almost empty refill it with some gas. Change or check the gap on plugs, and re gap them if necessary. A boost leak would maybe cause black smoke to come out, as your losing metered air somewhere in the system, thus the car burning more fuel then it should be. Do you have a wideband on the car? If you have evo scan, you can check your front 02 sensor with your computer and tactrix cable, just pull the voltage on it, make sure its not dead, make sure it changes voltage and doesnt just stick on one point. Or that could also be an issue.