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Thread: Idle - TPS Voltage Threshold

  1. #21
    Senior Tuner mowton's Avatar
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    Quote Originally Posted by LaTechGTO View Post
    Thanks! Yeah, it is definitely much easier than I thought; As you have probably noticed, I have a nasty habit of overcomplicating things haha. I think the biggest things for me was keeping the nomenclature and roles for each item - realizing a lot of different values are treated as adders to make up the Base Idle Airflow, and that the logged Desired Idle Airflow accounts for all of these and should be pasted directly into the Base Running Airflow table in order to account for the adjustments being made by the STIT and LTIT, ultimately resulting in close-to-zero STIT and LTIT. From what I am seeing, the Desired Airflow only correlates to the desired airflow through the IAC, not for the engine - this was another point of confusion to me early on. -- Just to clarify, the Base Running Airflow is not just the air going through the IAC, its the air being injested by the throttle blade opening as well as the IAC based on the IAC count. Thats why as you move you IAC counts up and down, so must you adjust you BRAF to get the LTIT and STIT closest to 0. I tend to want them to be slightly negative like .2/.5.

    Is there a target STIT value? I see most people like to run negative STITs as long as it doesn't cause any forms of "cruise control" becuase it ensures the engine is getting plenty of air between throttle transitions instead of stumbling/hunting for idle. Then again, I would think it would be best to have this as close to 0 as possible (negative or positive, no difference) since there are other tables that can be modified to aid in the previous idle issue scenario. -- See above

    I am still not sure how to adjust for the IAC effective area, and the reading I have done surrounding this topic basically suggests a few things 1) the IAC hole in the TB is much smaller on aftermarket TBs, necessitating either a change in the effective area vs IAC steps or by modifying the hole to allow easier airflow to the IAC 2) getting the IAC counts as low as possible since it seems to be much more accurate in the lower flow scenarios 3.) the changes being made are more of guess work than science. I think the ultimate reason for this is to make the dynamic flow match the anticipated flow, correct? I don't think I said that right, but basically for the IAC steps (anticipated area by IAC position = certain amount of airflow) to correlate to the actual flow going through it, which alows easy, mythodical adjustment later for idle tuning while moving. -- This is how I was taught, if you look at a stock IAC effective table, you will see it is all zero's to 12 mm2 IIRC. That means that no steps are required and the base throttle blade opening (with the blade hole) is equal to about 12mm2 for the 78mm stock throttle body. Now that changes of course as you readjust the setscrew or go with a larger TB (i.e a 90MM would be closer to 24-26mm2). So the way it works is the PCM generates a mm2 airflow requirement based on the sum total or Idle Desired air and adjusts the IAC IAW the mm2 calculation. The desired IAC count at idle is like 60-80 for stock and 40-60 for a cam (depending on its specs). While it isnt a scientific theorem, there is some intelligence to the tuning, more intuitive I would say.

    I am still hung up wondering if the NBs are actually adjusting for the anticipated stoich for the E10 fuel. I was always under the impression they targeted the stoich saved in the tune, not lambda = 1 for the fuel being used. In my mind, this would remove the need for a flex fuel sensor unless in OL. Maybe they do target Lamba = 1 for all different types of fuel while in CL (within the window for the NBs), hence the seemingly rich state I was noticing on the WB readings. -- All O2 sensors (WB or NB) all operate in Lambda and actual monitor Oxygen Molecules. The PCM and Wideband meters actually "convert" it to an AFR, which as you can see, you must define. Lambda 1.0 (stoich) is determined to be the most efficient burn. .9 is richer and 1.1 is leaner. Remember the desired Lambda for pure gas (AFR 14.7) is 1.0 and for E85 (AFR 9.3) is 1.0 as well. That is why Lambda is so much easier to tune by. The NB is only accurate around a very small window aroundstoich so it can't be used for enrichments in the .7/.8 area so widebands are used.

    Also, for those that are reading, I stated something earlier about "In Gear STIT" - There isn't such a thing; STIT doesn't care if you are In Gear or in P/N; only LTITs care since the values for each could be very different. -- True

    Thought I was done, didn't you? LOL
    2004 Vette Coupe, LS2, MN6, Vararam, ARH/CATs, Ti's, 4:10, Trickflow 215, 30# SVO, Vette Doctors Cam, Fast 90/90, DD McLeod, DTE Brace, Hurst shifter, Bilsteins etc. 480/430

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  2. #22
    I didn't see it answered, but with my 02 the most I can open the TB and still show 0% TPS is .76V. Which should be plenty if your IAC passage is big enough.

  3. #23
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    Thanks! Yeah, it is definitely much easier than I thought; As you have probably noticed, I have a nasty habit of overcomplicating things haha. I think the biggest things for me was keeping the nomenclature and roles for each item - realizing a lot of different values are treated as adders to make up the Base Idle Airflow, and that the logged Desired Idle Airflow accounts for all of these and should be pasted directly into the Base Running Airflow table in order to account for the adjustments being made by the STIT and LTIT, ultimately resulting in close-to-zero STIT and LTIT. From what I am seeing, the Desired Airflow only correlates to the desired airflow through the IAC, not for the engine - this was another point of confusion to me early on. -- Just to clarify, the Base Running Airflow is not just the air going through the IAC, its the air being injested by the throttle blade opening as well as the IAC based on the IAC count. Thats why as you move you IAC counts up and down, so must you adjust you BRAF to get the LTIT and STIT closest to 0. I tend to want them to be slightly negative like .2/.5.
    See, now I am confused even more on this item. Keeping all things the same (RPM, Fuel, AFR, timing, etc), wouldn't the desired airflow demand for the engine remain the same even if you adjust your TB/ IAC counts by adjusting the TB blade screw as long as your IAC isn't maxxed or bottomed out in either case. Does this have something to do with the need to alter the IAC effective area? Where my confusion lies is between the first and second image below where the only change was that I opened the blade to bring the IAC counts down; this is what made me think it's only flow through the IAC.

    Idle Log 1.JPG

    Idle Log 2.JPG

    I am still not sure how to adjust for the IAC effective area, and the reading I have done surrounding this topic basically suggests a few things 1) the IAC hole in the TB is much smaller on aftermarket TBs, necessitating either a change in the effective area vs IAC steps or by modifying the hole to allow easier airflow to the IAC 2) getting the IAC counts as low as possible since it seems to be much more accurate in the lower flow scenarios 3.) the changes being made are more of guess work than science. I think the ultimate reason for this is to make the dynamic flow match the anticipated flow, correct? I don't think I said that right, but basically for the IAC steps (anticipated area by IAC position = certain amount of airflow) to correlate to the actual flow going through it, which alows easy, mythodical adjustment later for idle tuning while moving. -- This is how I was taught, if you look at a stock IAC effective table, you will see it is all zero's to 12 mm2 IIRC. That means that no steps are required and the base throttle blade opening (with the blade hole) is equal to about 12mm2 for the 78mm stock throttle body. Now that changes of course as you readjust the setscrew or go with a larger TB (i.e a 90MM would be closer to 24-26mm2). So the way it works is the PCM generates a mm2 airflow requirement based on the sum total or Idle Desired air and adjusts the IAC IAW the mm2 calculation. The desired IAC count at idle is like 60-80 for stock and 40-60 for a cam (depending on its specs). While it isnt a scientific theorem, there is some intelligence to the tuning, more intuitive I would say.
    Great information, but still after reading that, I don't have a clue where to start by guessing the area of the opening on my NW 102 TB. IAW?

    I am still hung up wondering if the NBs are actually adjusting for the anticipated stoich for the E10 fuel. I was always under the impression they targeted the stoich saved in the tune, not lambda = 1 for the fuel being used. In my mind, this would remove the need for a flex fuel sensor unless in OL. Maybe they do target Lamba = 1 for all different types of fuel while in CL (within the window for the NBs), hence the seemingly rich state I was noticing on the WB readings. -- All O2 sensors (WB or NB) all operate in Lambda and actual monitor Oxygen Molecules. The PCM and Wideband meters actually "convert" it to an AFR, which as you can see, you must define. Lambda 1.0 (stoich) is determined to be the most efficient burn. .9 is richer and 1.1 is leaner. Remember the desired Lambda for pure gas (AFR 14.7) is 1.0 and for E85 (AFR 9.3) is 1.0 as well. That is why Lambda is so much easier to tune by. The NB is only accurate around a very small window aroundstoich so it can't be used for enrichments in the .7/.8 area so widebands are used.
    Sorry, I didn't convey what I was trying to say very well and in the process, said some very contradicting things. I knew it the PCM and WBs operated at Lambda, but I keep forgetting this all correlates to the same thing with all fuel - "OXYGEN" sensor So basically the only use for Commanded AFR (saved in the tune) is really just a set point to compare against when logging Actual vs Target. This should be much easier to work with once I get my Flex Fuel sensor installed and working; not sure it is going to work on my 04 GTO, but the rest of the parts should be here today.




    Thanks again for not losing hope with me!

  4. #24
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    Quote Originally Posted by JakeFusion View Post
    I didn't see it answered, but with my 02 the most I can open the TB and still show 0% TPS is .76V. Which should be plenty if your IAC passage is big enough.
    Good information! I should have checked to see when my TPS would stop recognizing 0% as well.

  5. #25
    Senior Tuner mowton's Avatar
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    So again as I understand it there are two theories I have seen....one is the tps resets itself back to 0% during each key off/key on start sequence or the reset procedure I stated above to reset closed throttle blade to 0%. I end up doing both to make sure....If voltage goes too high then a larger tb blade hole is in order..

    Ed M
    Last edited by mowton; 05-09-2015 at 09:58 AM.
    2004 Vette Coupe, LS2, MN6, Vararam, ARH/CATs, Ti's, 4:10, Trickflow 215, 30# SVO, Vette Doctors Cam, Fast 90/90, DD McLeod, DTE Brace, Hurst shifter, Bilsteins etc. 480/430

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  6. #26
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    Quote Originally Posted by mowton View Post
    So again as I understand it there are two theories I have seen....one is the tps resets itself back to 0% during each key off/key on start sequence or the reset procedure I stated above to reset closed throttle blade to 0%. I end up doing both to make sure....If voltage goes too high then a larger tb blade hole is in order..

    Ed M
    Yeah, I guess I should have clarified. I still use the normal reset procedure that you mentioned earlier, but what I was trying to say was that I wonder how far open I could adjust the TB (voltage and position-wise) and still return a 0% TPS signal as well as remain in Idle cells.

    Any input on the following items from before?

    1.)
    See, now I am confused even more on this item. Keeping all things the same (RPM, Fuel, AFR, timing, etc), wouldn't the desired airflow demand for the engine remain the same even if you adjust your TB/ IAC counts by adjusting the TB blade screw as long as your IAC isn't maxxed or bottomed out in either case. Does this have something to do with the need to alter the IAC effective area? Where my confusion lies is between the first and second image below where the only change was that I opened the blade to bring the IAC counts down; this is what made me think it's only flow through the IAC.

    Idle Log 1.JPG

    Idle Log 2.JPG
    2.)
    Great information, but still after reading that, I don't have a clue where to start by guessing the area of the opening on my NW 102 TB. IAW?
    Thanks!

  7. #27
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    Quote Originally Posted by mowton View Post
    Thats why as you move you IAC counts up and down, so must you adjust you BRAF to get the LTIT and STIT closest to 0. I tend to want them to be slightly negative like .2/.5.
    Is this in lb/hr or g/sec? I'm guessing the latter since we have spoken primarily in g/sec, but I just wanted to make sure.

    After doing more tuning, I finally got a chance to start tuning In-Gear idle, and whatdya know, the LTIT value started adjusting (now VERY close to zero).


    Any input on the following items from before?:

    1.) See, now I am confused even more on this item. Keeping all things the same (RPM, Fuel, AFR, timing, etc), wouldn't the desired airflow demand for the engine remain the same even if you adjust your TB/ IAC counts by adjusting the TB blade screw as long as your IAC isn't maxxed or bottomed out in either case. Does this have something to do with the need to alter the IAC effective area? Where my confusion lies is between the first and second image below where the only change was that I opened the blade to bring the IAC counts down; this is what made me think it's only flow through the IAC.

    2.) Great information, but still after reading that, I don't have a clue where to start by guessing the area of the opening on my NW 102 TB. IAW?
    I am very interested in dialing in the effective area if you don't mind trying to explain it to me

    One of the biggest impacts I received was converting the tune back to an older version and getting out of the Beta editor. I was experiencing some REALLY weird idle issues (Ex. Desired RPM values), and as soon as I uploaded an older file version with the non-Beta version, the quirks went away.

    PS - The car did alright at the heartbreaker Bristol Dragway; DA was ~2,500ft. While there, I slowly leaned out the AFR from 9.5:1 to 10.5:1, and I still have a little ways to go before I reach my commanded AFR (11.2:1). I also got my shift points closer, but I still have 2-300 rpms to go in each upshift. I ran out of gear on the big-end so I will need to install some 28" tires because I'm seeing around 8% converter slip; I am bumping my 6,990 rev limiter as I cross the line @ 140mph. I don't think it's too shabby for a true street car I drive to/from the track with a full interior; 3,880# without me in it.

  8. #28
    Senior Tuner mowton's Avatar
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    sorry have been really busy lately.....will post a response tonight

    Ed M
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  9. #29
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    Quote Originally Posted by mowton View Post
    sorry have been really busy lately.....will post a response tonight

    Ed M
    No worries... I completely understand. I've been swamped for the past few weeks until today Just a short breath of fresh air before I have to get back at it again!