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02 sensors. which ones to replace first?will it help?

This is a discussion on 02 sensors. which ones to replace first?will it help? within the General Help forums, part of the LSx Technical Help Section category; Got a 99 z28 with 113k on it no ses light, runs good but I have no idea when the ...

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    poor bastard DaytonaBlues's Avatar
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    02 sensors. which ones to replace first?will it help?

    Got a 99 z28 with 113k on it no ses light, runs good but I have no idea when the o2 sensors were replaced last and I was going to go ahead and change out the upstream ones first and not bother with the two down streams. The car like I siad has no ses or check engine light on just wanted to change em for good measure. Should I even bother or change the downstream ones first?

    I'm also kinda curious as to when its time to replace the catalytic converters since those too are original. I live in massachussettes and the emmisions laws suck asscheek so I got a run em. I'm trying to get the car to idle better and ima new Ls1 owner but its my fifthfbody and I knw when it comes to cats no one probably knows if it matters how cheap they are like these I found on eBay

    Stainless Steel Direct Fit Catalytic Converter by Maremont 652162 | eBay
    Stainless Steel Direct Fit Catalytic Converter by Maremont 652161 | eBay
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    The upstream O2 senders are what control fueling. Good for around 80,000 miles. The downstream O2 senders simply tell the PCM if the cats are working properly. Unless you are getting a code for the rear ones, don't waste your $$.

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    None Shall Pass Knight's Avatar
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    Agree with Jeff. You also state you're trying to get the car to idle better? You might try cleaning the MAF with some CRC cleaner also.

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    okay so I should probably replace the fronts and not worry about the rears.
    I know there are a million different manufacturers of o2 sensors and I can get them for about 32 bucks a piece from Rock auto.com Denso O2 sensors any good?

    And CRC the mass air sensor? Mine is unfortunatly a stock descreened MAF. U think its a good idea to douche the mass air sensor in CRC?
    Otherwise I'm kinda blaming some Idle quality on the pcv which I converted to use the the new fixed orifice type, and I converted the valve so it sits upright to help keep any more oil outta my intake. Basically, 113k miles and I think every sensor is stocks and has never been replaced I'm definitely going to replace the front o2 sensors for now

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    Descreening the MAF alters its calibration and throws off air reporting to the PCM. Never mess with the MAF, other than to clean it as recommended by Knight. Over time, the tiny wires on the MAF end up coated with particles that insulate them from the incoming air, especially if you run a cotton gauze oiled air filter element. This also affects air reporting and throws off fueling. Our car came with a descreened and debladed MAFwhen we bought it... and also an off idle stumble that was remedied only by replacing the MAF.
    JayTA98 likes this.

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    poor bastard DaytonaBlues's Avatar
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    Quote Originally Posted by pajeff02 View Post
    Descreening the MAF alters its calibration and throws off air reporting to the PCM. Never mess with the MAF, other than to clean it as recommended by Knight. Over time, the tiny wires on the MAF end up coated with particles that insulate them from the incoming air, especially if you run a cotton gauze oiled air filter element. This also affects air reporting and throws off fueling. Our car came with a descreened and debladed MAFwhen we bought it... and also an off idle stumble that was remedied only by replacing the MAF.
    OK, we'll I'm SCREWED.my maf is descreened even though I bought the car like this. So how can I clean the wires inside short of me replacing the entire maf sensor. What if anything can I buy that I can spray on the small wiresinside to help get the maf clean? I know crc does make something called mass airflow cleaner if I'm not mistaken so what should I do?? I'm really worried now because I do run a oiled K and N air filter so I'm sure those fine wires inside the maf are filthy and covered with goo. Great,now i'm afraid I need a new maf since the dummy before me took the screens out.

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    Quote Originally Posted by DaytonaBlues View Post
    Quote Originally Posted by pajeff02 View Post
    Descreening the MAF alters its calibration and throws off air reporting to the PCM. Never mess with the MAF, other than to clean it as recommended by Knight. Over time, the tiny wires on the MAF end up coated with particles that insulate them from the incoming air, especially if you run a cotton gauze oiled air filter element. This also affects air reporting and throws off fueling. Our car came with a descreened and debladed MAFwhen we bought it... and also an off idle stumble that was remedied only by replacing the MAF.
    OK, we'll I'm SCREWED.my maf is descreened even though I bought the car like this. So how can I clean the wires inside short of me replacing the entire maf sensor. What if anything can I buy that I can spray on the small wiresinside to help get the maf clean? I know crc does make something called mass airflow cleaner if I'm not mistaken so what should I do?? I'm really worried now because I do run a oiled K and N air filter so I'm sure those fine wires inside the maf are filthy and covered with goo. Great,now i'm afraid I need a new maf since the dummy before me took the screens out.
    I would just forget the MAF and get an SD tune . That is what I did.
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    Quote Originally Posted by DaytonaBlues View Post
    OK, we'll I'm SCREWED.my maf is descreened even though I bought the car like this. So how can I clean the wires inside short of me replacing the entire maf sensor. What if anything can I buy that I can spray on the small wiresinside to help get the maf clean? I know crc does make something called mass airflow cleaner if I'm not mistaken so what should I do?? I'm really worried now because I do run a oiled K and N air filter so I'm sure those fine wires inside the maf are filthy and covered with goo. Great,now i'm afraid I need a new maf since the dummy before me took the screens out.

    I would clean the MAF and see what happens. From what I have read, the error is probably less than 5% with the screen removed and feedback from the O2 senders will compensate for this. Who knows how long the prior owner ran our car with the MAF hacked up.

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    Agree with Jeff and Walt. Let us know how you make out.

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    I made out okay I cleaned the mass airflow sensor out and the difference is somewhat noticeable but now I'm considering replacing my catalytic converters. the problem is I really have no idea how to know if they are still flowing good. I'm considering buying a scan tool and.maybe looking at the o2 sensor voltages to see if they are high or.low.or.what.? Any ideas how to check cats?

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    If you scan the car, and you get "CATALYTIC CONVERTER EFFICIENCY" codes, then it's time to replace them.

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    ^^ This (so long as the senders are not defective), or if you have a rattling sound in the exhaust, your mileage and performance both drop at the same time, or chucks of converter are blowing out the tailpipe.

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