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Thread: High IAT's killing my AFR

  1. #1
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    High IAT's killing my AFR

    It has been HOT the last few days and this has messed with my AFRs. I'm running the 2Bar OS on my 2012 Corvette, stock engine with vortech supercharger. I have two plots with different IAT's, and I picked an RPM to compare. I have some quick data of the compare below. The air related stuff seems to have about an 8-9% drop in it. Which is about what I would expect given the 30*F air temp change. But the Cylinder mass and the wideband readings have a 25% swing. It seems the cylinder mass is used to calculate the injector pulse that is giving me the bad AFR. How is the cylinder mass calculated? I'm sure there is a table I could adjust to compensate for this, but I would have thought that these temps would have been within what the stock settings could handle. A large swing like that doesn't make sense to me, is there something I'm missing? Any advice, insight, or guidance would be helpful.


    Here are the interesting things I noticed between the two different runs, cold vs hot.

    85 109 Manifold Air Temp
    180 203 ECT
    3400 3400 RPM
    124.0 124.0 MAP
    216.9 200.2 MAF
    220.5 202.2 VE(g/s)
    220.9 203.4 Dynamic Air
    0.98 0.74 Cylinder Mass
    0.768 1.001 Wideband
    9.54 7.08 injector pulse(ms)
    Normal Hispeed AirCalc Mode
    Pass Failed MAF State
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  2. #2
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    Something nasty is going on. Double check your MAF settings.

    Screenshot 2022-06-25 213546.png

  3. #3
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    Quote Originally Posted by hjtrbo View Post
    Something nasty is going on. Double check your MAF settings.

    Screenshot 2022-06-25 213546.png
    I did notice that weird drop in Dynamic VE when the OS switches from NORMAL to HI-SPEED modes. The odd thing is that there is no corresponding AFR change that I would have expected to go with that. I tried to use the data points before the transition to figure out the lower RPM change in AFR, but maybe this is a clue to a larger problem.

    I looked at my MAF calibrations and there isn't anything that jumped out at me. I've attached the file if someone can see something I can't.
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    Last edited by mn_vette; 06-25-2022 at 07:44 AM.

  4. #4
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    why is your estimated map max reading so high ? its above the map sensor settings, dont think it will affect it just noticed it, also your 02 sensors are doing strange things one looks stuck or unplugged the other is cycling/following during your WOT run u can see it showing leaner as well, if u have unplugged one for the wideband some ecu dont like that and can do strange things

  5. #5
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    also most of your prediction coefficient tables are zeroed out which prob wont work well with the maf/ve blend, if u have stock tune put those back in and see if it helps

  6. #6
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    Quote Originally Posted by 07GTS View Post
    why is your estimated map max reading so high ? its above the map sensor settings, dont think it will affect it just noticed it, also your 02 sensors are doing strange things one looks stuck or unplugged the other is cycling/following during your WOT run u can see it showing leaner as well, if u have unplugged one for the wideband some ecu dont like that and can do strange things
    I did unplug one of the O2 sensors to do the wideband. There hasn't been an opening in the shop to get a new bung welded in yet. The MAP is a ZR-1 map sensor, so it should have a higher reading capability for boost. Sorry, I should have mentioned those in the original post.




    The prediction coefficients I kept the same as the stock vehicle. They haven't been touched.
    Last edited by mn_vette; 06-25-2022 at 08:33 AM.

  7. #7
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    thats strange they are zeroed out, the sensor offsets are fine its the estimated max value is like 1700kpa should be like 200kpa, if u take out the 02 just leave it plugged in and hanging there tied up but remember they do get hot so tie it up in a safe spot, then see if its any better

  8. #8
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    Quote Originally Posted by 07GTS View Post
    thats strange they are zeroed out, the sensor offsets are fine its the estimated max value is like 1700kpa should be like 200kpa, if u take out the 02 just leave it plugged in and hanging there tied up but remember they do get hot so tie it up in a safe spot, then see if its any better
    I connected the O2 sensor back and it stopped complaining about electrical faults on my digital display. I also changed the max MAP from 255psi to 255kpa. The original guy that did the starter tune must have had the wrong units or something.

    I took a few more runs. The first one is me pulling out of my garage, driving for about 10 minutes, then recording. The "more" plot is a after stopping for a while and leaving the car outside in the sun. I still seem to be getting some weird stuff in the speed density area. The MAF, high rpm area, seems to be less consistent. Any help you might have would be appreciated.



    EDIT: the more I stare at this stuff it seems like my MAF(g/s) and my VE(g/s) are tracking fairly closely, but my Cylinder airmass seems to not be changing as it should. And when the Cylinder Airmass changes there is a drastic change in the AFR. How is Cylinder Airmass calculated? I've googled it and gotten some general things, but does someone have a detailed description with which variables I can log to show what is happening?
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    Last edited by mn_vette; 06-25-2022 at 05:57 PM.

  9. #9
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    Doesn't like the blend.

    Drop the disable / re-enable to 1800 / 1600

    And put in this VE table. This is based off your old tune so just copy tables mentioned above across so the things you fixed up from 07GTS changes aren't lost.

    See how it goes. If it still does I'm out.
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    I did some runs this morning in the cool air, about 75*F out, kind of humid. My tune did just fine, no issues with the AFR(although I did have something very weird happen with my timing on the second WOT in that log). I ran the test tune from hjtrbo, all the same goodness. I changed that tune to disable the MAF and do speed density only. Things got really rich here, but consistent.

    Now for the fun part. I know this 2Bar OS has a bug that if you turn off the car and restart it quickly it messes with a lot of things. I tried that and I got some bad stuff happening again. It looks very similar to the problems I had at hot. The speed density portion is going pretty lean, there is a dip in dynamic air when it switches over to HI-SPEED mode at 4k rpm even though it is set to something else, the MAF is no longer failed. So what I think is happening is that there might be something else tripping this bug other than a quick restart. Something to do with the car sitting in the sun all day or getting hot. I'm not sure what this could be, but something.


    Log Files:
    16_cool_morning: My base tune doing just fine
    TEST_MAF: hjtrbo's tune running on MAF
    TEST_MAP: hjtrbo's tune with MAF disabled
    TEST_MAP_quick_restart: Quick restart invoking 2Bar OS bug
    Last edited by mn_vette; 06-26-2022 at 07:38 AM.

  11. #11
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    did u write entire when u changed to the 2 bar OS ?

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    Quote Originally Posted by 07GTS View Post
    did u write entire when u changed to the 2 bar OS ?
    Oh yes, I followed this list of instructions from the HPtuners website. https://www.hptuners.com/help/vcm_ed...ters_gm_os.htm

    Bold letters stating that I needed to write the entire ECU. It took quite a bit longer to flash the entire thing.

    It definitely does not update the barometric pressure at WOT anymore, which is the main reason I went with this OS.

    I can try re-flashing the entire thing again to see if that does anything. I'm willing to try anything at this point.

    EDIT: I did a read of the entire ECU and it came back as the 2 BAR OS. This seemed like a better verification than a re-flash and more testing.
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    Last edited by mn_vette; 06-26-2022 at 08:34 AM.

  13. #13
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    as far as im aware the e38 didnt update the baro it was only when u key on it uses the map value for baro before the engine starts, the e67 i think had some odd baro things going on, it wont be anything temp related doing it unless its a poor connection somewhere or issue with the ecu, have u tried going back to the factory OS and see if it still does it ?

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    Quote Originally Posted by 07GTS View Post
    as far as im aware the e38 didnt update the baro it was only when u key on it uses the map value for baro before the engine starts, the e67 i think had some odd baro things going on, it wont be anything temp related doing it unless its a poor connection somewhere or issue with the ecu, have u tried going back to the factory OS and see if it still does it ?

    OK, so I took a step back and refined my testing method. I am now doing 2nd gear pulls starting at about 25mph. This gives a good clean RPM curve. I think I might have been getting some things messed up with letting the car downshift itself. I did a pair of runs for each of the following:

    2 Bar OS MAF enabled Dynamic set to 5,000 rpm
    2 Bar OS MAF Disabled, MAP only
    Original OS MAF enabled Dynamic set to 5,000 rpm (Everything copied over from 2Bar OS except VE table, used last best VE for this OS)
    Original OS MAF Disabled, MAP only
    Original OS MAF enabled Dynamic set to 1,000 rpm


    things I noticed.
    1.) the creeping AFR happens both times that the MAF is enabled
    2.) even though the dynamic range is set to start at 5,000 RPM it will switch around 4,000 rpm. This happens for both the 2 Bar and the Original OS.
    3.) The MAF only plot has AFR lean at about 6% in the same spots that the "blended" one has it at about 20%.


    So it really looks like I'm having issues with the blending between the two methods. If my VE table is pretty close and my MAF setting are pretty close when they are done individually, what would cause them to get so wonky when I try to use both together? Are there some tricks I should know about on how to do this?

    EDIT: I put in a snippet from one of my plots. 3,500 RPM where we should be using blended, but the Dynamic Air looks like it is just following the general trend of the MAF and not using the VE much at all. Maybe I need a better understanding of how this is calculated in the computer.

    Snippet.JPG
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    Last edited by mn_vette; 06-26-2022 at 05:02 PM.

  15. #15
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    Goodness its a mess, it hates life on the MAF. What it looks like to me is the correlation between MAF and SD airflows is miles away.

    MAF is located after the charger? In a straight run of pipe with no interferences?

    I think your best course with what you've got in front of you would be straight out SD on the custom OS and never look back.

  16. #16
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    I would have ditched the MAF a long time ago.

    Where the MAF is located and the turbulence it sees will make a huge difference in fueling.
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    Snippet2.JPG


    MAF is in the stock location, but with the supercharger it has a few other things. The Intercooler is about 18" wide that goes into a 4" pipe then a 45 degree angle about 6 inches before the MAF. I can go back to the speed density only. I was hoping to keep the MAF to make it more consistent over weather changes, but it seems like that isn't going to work.

  18. #18
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    MAf won't make it more, or less, consistent even if it's not reading messed-up air.

  19. #19
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    Quote Originally Posted by mn_vette View Post
    Snippet2.JPG


    MAF is in the stock location, but with the supercharger it has a few other things. The Intercooler is about 18" wide that goes into a 4" pipe then a 45 degree angle about 6 inches before the MAF. I can go back to the speed density only. I was hoping to keep the MAF to make it more consistent over weather changes, but it seems like that isn't going to work.
    Yeah, I understand.. but that tube isn't stock. They are just too noisy. You'd have a better result in SD.
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  20. #20
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    Quote Originally Posted by Alvin View Post
    Yeah, I understand.. but that tube isn't stock. They are just too noisy. You'd have a better result in SD.


    Thanks for the help everybody. I appreciate it. I know I was pretty far off in the weeds when I started this thread. But I'm glad you guys got me straightened out.