will01z28

i have an 01 stock z28 and i usually fill up at about 1/4 tank. When i first got the car i would get about 210 to 220 miles (from full to 1/4). I changed the spark plugs at about 95000. I put in bosch platinum plus 2 plugs and almost right away i noticed i was only getting about 160 to 170 (from full to 1/4) and straight highway driving wasnt much better. A few weeks ago i put in acdelco irridium plugs and changed the fuel filter and im still getting the same bad milage. any suggestions as to what else might be killing my milage?

xX-Z28-Xx

iTrader: (4)

Maybe the wot times are in the books now....

hammertime

iTrader: (1)

I would not suspect two different plugs would give you poor mileage. If you have access to a scanner, you might look into how healthy your O2 sensors are. They usually degrage over time, and at 95k, may be a good place to start. Other ideas:

1) Cold weather, cold start enrichment, idling to warm the car
2) Oxygenated / Winter Blend Fuels
3) 1/4 Tank on the gauge isn't entirely accurate. Have you actually calculated your mileage from the distance traveled/gallons consumed?
4) Driving Style

All the combined changes may be just enough to drag your mileage down a few MPG's

will01z28

its been doing this since about may 2010 and i live in florida so there isnt a lot of cold weather. I even filled up with ethenol free gas a few times and still no difference, and my driving style is a little bit easier then it used to be, and when it gets to 1/4 tank it usually takes about 10 to 10.5 gallons to fill back up every time. so i guess the only thing left to do is check the o2 sensors. if they were bad would my check engine light come on?

nghisus

It all depends on the level of degradation. You should fill up your tank, reset your trip counter, drive until 1/4 tank. Fill it back up to full, take what your trip counter says and divide by how much you put in to get a more accurate measurement in miles per gallon. I know you're waiting until a 1/4 of a tank but 1/4 tank is very qualitative.