urbex Posted June 13, 2011 Report Share Posted June 13, 2011 Hey...I have a quick question. I tried searching both on this forum and on Google with no luck. While driving home yesterday I had my OBDII scanner plugged in so I could see live data as I drove, just in case the "surging" would act up. Well, it never did on the way home, but I did notice that while driving the O2 sensor readings would vary quite a bit! At times the first o2 sensor (I'm guessing upstream?) would read anywhere from .5-.7, but then at times would drop to as low as .08. When it would go that low, the second o2 sensor would be anywhere around .4 or even .3. Now, I'm thinking the second readings were normal, but should the first one be going that low? Also, at times the first sensor would have a lower value than the second? I thought the second should be lower? If someone could help clarify this for me, it'd be greatly appreciated! I know I read somewhere that a bad o2 sensor can give surging issues, so I'm just trying to check everything. (Although thanks to PsychoMatt, I have a set of coil packs I'm putting on today to see if that clears it up! ) Thanks guys! Quote Link to comment Share on other sites More sharing options...
AL Posted June 13, 2011 Report Share Posted June 13, 2011 The first 02 sensor should drop below .2 and go above .8... What you saw is perfectly normal... below .5 is lean and above .5 is rich... And as for the rear 02 sensor it should be above .3 and below .7 for cat efficiency check Quote Link to comment Share on other sites More sharing options...
urbex Posted June 13, 2011 Author Report Share Posted June 13, 2011 Ok, thanks Al! I just wanted to be sure what I was seeing is normal! FWIW, I did notice I was going downhill when it was doing that, so that would make sense! Thanks again! Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted June 14, 2011 Report Share Posted June 14, 2011 completely normal operation. the PCM purposely drives the engine both richer and leaner than stoich constantly, which is why you'll see the O2 "swing" high and low. generally, if your fuel trims aren't acting up, the swings should center around ~.45 volts. Quote Link to comment Share on other sites More sharing options...
urbex Posted June 14, 2011 Author Report Share Posted June 14, 2011 Yeah, and that's typically where they were reading on average I noticed. But yeah, my fuel trims have been pretty close to 0, the long term being slightly lean, but only by a point or two. I think that just has to do with my driving style more than anything (being light on the gas and coasting) Quote Link to comment Share on other sites More sharing options...
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