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99 z28 lag/stutter please help!!

This is a discussion on 99 z28 lag/stutter please help!! within the General Help forums, part of the LSx Technical Help Section category; I have never vacuum tested our car and am uncertain what it should be. You have an EGR setup on ...

  1. #21
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    I have never vacuum tested our car and am uncertain what it should be.

    You have an EGR setup on your car? If so, that is another good suspect for an off idle hesitation. If it is dumping exhaust into the intake at low rpm that can cause issues. On older cars, you could watch the pintle move on the EGR valve and see if it was opening early or hanging open. Not sure about these as our car does not have an EGR valve.

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    Senior Member Too Fast's Avatar
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    I've had a stumble/misfire the past year, only once was it bad enought to set a misfire code. I didn't get it scanned in time to see which cylinder it was. I could feel it at idle sometimes, and sometimes a little when cruising or lightly accelerating. Turned out to be a partially flowing fuel injector. I had them tested and 7 were perfect, the 8th was about 65% flow of the others.

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    Junior Member clewis05's Avatar
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    Well guys I'm still not finding anything out of the ordinary. My scan tool should be here by Friday so hopefully it'll tell me something that I don't know. To answer your question Jeff I do have the EGR system still on but I'm def looking to delete it all to clean up the engine bay. But I been trying to read up the how to's just to make sure I do it all right without jacking something up hahaha. I'll keep ya all updated, if you all can think of something else let me know. Thanks

    Click for full size 1999 CHEVY CAMARO Z28 M6 LS1 PACESETTER LT 3" ORY TUNED BY FROST

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    You can simply remove the system and cap the holes. A block off kit from Hawk's runs under $50. However, you will need to send in your PCM for a mail order tune to have the codes "turned off". This will keep your SES light off.

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    Junior Member clewis05's Avatar
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    Damn wish I did this before i sent it to Frost to be tuned already FML Well I been looking for a LS6 intake for a good price, so hopefully i find one then Ill remove the EGR system and get a re-tune

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    Junior Member clewis05's Avatar
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    Attachment 25823 ok guys here is some live data that I just scanned while the car was running. It is telling me to replace my MAF sensor. Could that be the issue? I did try cleaning it just maybe thats the issue. What you all think?

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    Your bank one fuel trims are maxed -- meaning the PCM thinks it needs to dump in more fuel. It also looks like your bank one O2 sensor isn't showing any volts. The sensor data should be rapidly bouncing up and down between 100 and 800 mV with the engine in closed loop and up to temp. Looks like an issue with the driver side pre-cat O2 sender or wiring.

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    Junior Member clewis05's Avatar
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    With all that being said how do I go about looking into that issue? I have no cats on the car. Its a brand new O2. I have an extension wire for the LT headers I have. Have no clue what you mean when you say sender. What does all of this mean anyways?
    O2S11(V) 0.000
    ST FTRM11(%) 51.6
    O2S12(V) 0.165
    O2S21(V) 0.640
    ST FTRM21(%) -0.8
    O2S22(V) 0.675

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    Extensions have been known to cause issues. Best bet is to run Bosch P/N 13111 Oxygen Sensors (also referred to as "O2 senders"). They come with a nice long harness and no extensions are required. Also, a "new part" does not always mean a good or working part -- I have taken many new parts back to the store over the years that simply do not work.

    Here's the breakdown:

    O2S11(V) 0.000 Bank One (driver side), Sensor One (pre-cat) O2 sender -- showing 0.000 mV (This is bad!)
    ST FTRM11(%) 51.6 Short Term Fuel Trim (driver side) -- adding 51.6% more fuel than called for in the tune (This is bad!)
    O2S12(V) 0.165 Bank One (driver side), Sensor Two (post-cat) -- just tells the PCM if the cats are working - may be tuned out.
    O2S21(V) 0.640 Bank Two (passenger side), Sensor One (pre-cat) -- looks ok.
    ST FTRM21(%) -0.8 Short Term Fuel Trim (passenger side) -- subtracting 0.8% -- this is good (number should be close to 0.0)
    O2S22(V) 0.675

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    Junior Member clewis05's Avatar
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    I hear ya on "new" part bc that O2 sensor I replaced twice bc I felt it wasn't working. So I'm hoping the chance of having 2 bad O2 in a row is slim to none. haha But I guess I'll give the Bosch ones a go and see what happens. Is there a specific place to order it from or just google it. Is it possible if the MAF is broke would that throw the numbers off on the O2 or is this simply an O2 issue all together? Thanks for breaking down the info above barney style lol

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    I do not see anything wrong with the MAF. An easy test is to swap the sensors from side to side. If the problem follows the sensor, you know it is the issue. If the problem stays on the driver side then it is likely the extension or the wire harness that is the issue.

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    Junior Member clewis05's Avatar
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    Alright. Ill try this tomorrow and run the scan on her again and see what happens. The O2 can cause a lag/sputter like what I have described? Btw I looked up that P/N on the Bosch and its saying it doesn't fit my car. Is that true?

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    The parts store will try to sell you P/N 13444. The P/N 13111 are the Corvette sensors and that is what you want. I have been running a set in our car for the past 4 years or so with zero issues, and lots of guys on here have them in their cars. Your issue is almost certainly an overfueling problem caused by a problem with the O2 sender or wiring. Only other thing that would cause the car to dump fuel like that would be outside air entering the exhaust stream above the O2 sender which makes the PCM think you have a lean condition. Your fuel trims are hugely out of whack - again, the trims should be running close to zero when everything is working correctly. On our car, I think STFT's ran from 0.8% to 1.8% last time I looked. The trims can also run negative which simply means fuel is being subtracted, but again the number should be close to zero... lets say within the range of -3.0 to 3.0 for a good tune.

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    Junior Member clewis05's Avatar
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    Quote Originally Posted by pajeff02 View Post
    The parts store will try to sell you P/N 13444. The P/N 13111 are the Corvette sensors and that is what you want. I have been running a set in our car for the past 4 years or so with zero issues, and lots of guys on here have them in their cars. Your issue is almost certainly an overfueling problem caused by a problem with the O2 sender or wiring. Only other thing that would cause the car to dump fuel like that would be outside air entering the exhaust stream above the O2 sender which makes the PCM think you have a lean condition. Your fuel trims are hugely out of whack - again, the trims should be running close to zero when everything is working correctly. On our car, I think STFT's ran from 0.8% to 1.8% last time I looked. The trims can also run negative which simply means fuel is being subtracted, but again the number should be close to zero... lets say within the range of -3.0 to 3.0 for a good tune.
    Sorry it took so long to get back been busy. Anyways thanks for the heads up. I'll def be getting those in the near future if its the O2 or O2 extension wire. Im going to attach the second scan test after I switched around my O2's. You tell me what you think. I was trying to compare the 1st test to the 2nd and the % looks alot lower if I was reading it properly. The codes it has thrown all point in telling me to replace my MAF sensor. I unplugged the MAF this morning and took it for a drive. It all did seem ALOT better. The lag wasn't there when slightly pressing the gas atleast not as bad as it was. So you think maybe it is the MAF sensor that needs to be replaced. I'm thinking about replacing the MAF and going from there just don't want to throw a $100 away if I don't need to. Let me know what ya think. Attachment 25825

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    Your Bank 1 trims are still way out of whack and your driver side O2 is still showing no volts.

    I do not think your MAF is the issue.

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    Ok. You want me to switch the O2 extensions now and see what that does? To find out if its the O2 extensions. If the MAF was jacked would it throw off my trims as well? Whats your suggestions now?

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    If the MAF was acting up, there is no way only one bank would be calling for more fuel. Again, the "0.00" mV reading for the O2 sender on the driver side, together with the maxed out fuel trim on that side, is a dead give away as to the problem.

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    Junior Member clewis05's Avatar
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    Ok. We'll the next step I'll try is swapping around the O2 extensions and see what that does. Thinking about installing a vacuum gauge so I can monitor if I have a leak or not. Hopefully I find the damn problem soon

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    A functioning O2 sender will rapidly cycle up and down -- it will never sit at zero.

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    So would that mean that there is something wrong with my extension or my O2? The problem stayed on the driver side right? So that meAns my extension is bad or something before it?

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