Hey guys, I need to know if O2 sensors can go "bad" or hurt gas mileage without throwing a code. I only replace O2 sensors when a code comes up. I've had my car for 3 years. I drove it ALL the time until last April when I got a work truck, then the Z became a weekend car with very little driving. Back in January, I started driving the car again on a regular basis and now I've noticed I lost signifigant gas mileage. Before, I would get 25-26 mpg on highway and 22 in the city. Now, no matter how I drive, I can't get more than 20 mpg. I went through the car and did a thorough tune-up. I replaced all fluids, and all filters including fuel and tranny filters. New plugs, cleaned the throttle body and MAF. The tune-up made my car idle and run a whole lot better, but did not affect the gas mileage. Last week, I jacked the tire pressure up from 32 to 40psi. Now, I'm BARELY getting 22mpg....and that's if I baby the car. Is there anything else that can affect gas mileage?...something that I missed? What about an "iffy" fuel pump? What about alignment? Tires? Gas for my car finally went over $4/gal. the other day so I'm trying to squeeze out all the mileage I can get. In advance, I really appreciate all the help and input.

 

When O2 sensors start to get lazy and go bad the PCM will trip a code for it. But there is no way of knowing how far gone they are at that point. The typical life of a O2 sensor performing correctly is about 75,000 miles. If yours ahave over that on them you would not be wasting your money to replace them, but there is no gaurentee you will get back your lost gas millage.

Pumping you tires up to 40psi is going to wear them out prematurely. I would return them to proper inflation pressures.

Re'

 

I noticed a similar decrease in mileage in the last year also. I seem to get that extra mileage back when I fill up at Sun or some place that is not using 10% ethanol. Here in Oklahoma it is not required nor is it required for the gas stations to tell us but the news ran a special a while back and informed us who was not cutting the gas with Ethanol.

 

ooooooooooooooh!.......I forgot all about the whole ethanol thing. Will that really hurt gas mileage? I usually get my gas from Shell or Chevron. I need to check their ethanol content.