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Thread: Greenhorn

  1. #21
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    Quote Originally Posted by ds8
    These are the ones I am using:
    Cool, I get out of here in bout 30 mins, I'll change my laptop and do a log on the way home . Would you mind looking at that later and telling me what you see?

  2. #22
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    I can do that for you. That'll be fun, thanks. If you can, do one longer log of normal driving and then do one short one where you drop the hammer and get max rpms out and hit 60-70 mph. don't beat on it for me though...only if you want to.

  3. #23
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    Not that I've seen it exactly spelled out but when logging should you be
    trying to get as many different acceleration and deceleration scenarios as you can or just drive like grandpa to the bingo hall?

  4. #24
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    Try to fill all the cells up on your knock map. Constants speeds can do that if you drive through hills. You can drive around changing the throttle to get all the cells, but you can induce burst knock into the knock table and can't remove that nor would you know that happened unless you watch. You have a couple other choices. Cruise control though hill terrain gives you constant speeds with varying load. Or, constant load as speed increases will fill up the tables horizontally. I find it easiest to hit the cruise and get the cells to fill up that way. When you have all of one column filled, adjust the speed some and get another column to start filling. I live where I can drive though plenty of hills and find on-ramps so it may not be as easy for you.

  5. #25
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    The VE table is actually indicating the engine's ability to completely fill the combustion chamber with air. It's nature is not to add fuel, it doesn't care about fuel. The VE tables are used to calculate the air/fuel charge.

    6 degrees of advance sounds way out there, but I guess it works for you.

    I am still confused as to the timing controlling AFR in closed-loop. The PCM already backs timing when it encounters knock while it is still toggling around stoich. KR has no effect on the commanded or actual AFR.

    I agree that pulling timing is easier than adding fuel to reduce KR, but 16 degrees seems extreme. Are you seeing 16 degrees of KR? Allow me to quote ds8 from 10-11-06 on another forum, "My knock retard was at 8* at RPMs greater than 1400 all the way to redline with MAP at or above 85 kpa. KR was at least 5* in the same RPM range with MAP at or aove 50 kpa."

    How about posting a screenshot of your 'low Rpm non-PE spark advance' table.

    I am not trying to be a pain, I just want to try and understand what you are doing.
    Last edited by blandmiller; November 22nd, 2006 at 10:30 AM.

  6. #26
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    I never said that commanded AFR changes knock, that is your supposition. AFR of 14.6 tells you that you are not in PE mode and that you should be taking out advance in the non-pe table.

    The VE table is actually indicating the engine's ability to completely fill the combustion chamber with air. It's nature is not to add fuel, it doesn't care about fuel. The VE tables are used to calculate the air/fuel charge.

    VE is really an arbitrary number since the I6 (pre-maf) doesn't know directly what mass/volume of air is really entering the intake. The air fuel charge is commanded to 14.6, but by chaing VE you can produce different true AFR's because the injectors pwm is determine by looking at a VE table based on load and RPM. Put in a higher VE value and the engine will run rich (on the wideband) even though the commanded AFR is still 14.6.

    I agree that pulling timing is easier than adding fuel to reduce KR, but 16 degrees seems extreme. Are you seeing 16 degrees of KR? Allow me to quote ds8 from 10-11-06 on another forum, "My knock retard was at 8* at RPMs greater than 1400 all the way to redline with MAP at or above 85 kpa. KR was at least 5* in the same RPM range with MAP at or aove 50 kpa."

    I think the max retard the pcm can command is 8 degrees. I have never seen more than that even though the timing was advanced 16 too far.
    I pulled 16 degrees out of the wait4me tune. The most I pulled out of the stock tune was 9 degrees and many of the fields were only 2 to 3, and I added a bit in a few cells. This is why the stock tune is far superior to the wait4me tune.

  7. #27
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    From today at around noon "Backing down the advance lets the engine run closer to 14.7 because there is no knock." What did you mean by this statement?

    VE is absolutely not an arbitrary number. A MAF sensor tells the PCM the amount of air passing through it (to the best of it's ability). The VE table is used to provide the same information, but it is not actually measuring the air. These tables are predicted airflow values from the factory and may not be as accurate as you think. I believe you are incorrect in assuming that changing the VE table will make the engine run rich when you are commanding 14.6. Normally, if you are commanding 14.6, you are (by your previous admission) in closed-loop (non-PE) and fueling is controlled by O2 sensor readings, LTFT, and STFT (and those pesky pv=nRT calculations).

    I have not seen any indication that the maximum KR range is 8 degrees. If this is true, it is good info. I do not believe I have ever seen more than 8 degrees of KR, but never assumed it was a max value. I will keep it in mind and see if it holds true in my tune.

    Just a thought, can you post a log file containing the KR of 8* from 1400 to redline? I have never seen anything like that.
    Last edited by blandmiller; November 22nd, 2006 at 11:16 AM.

  8. #28
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    From today at around noon "Backing down the advance lets the engine run closer to 14.7 because there is no knock." What did you mean by this statement?

    All that I am saying is that ICE's can be run rich to reduce knock or the advance can be reduced so the car can run leaner.


    VE is absolutely not an arbitrary number. A MAF sensor tells the PCM the amount of air passing through it (to the best of it's ability). The VE table is used to provide the same information, but it is not actually measuring the air. These tables are predicted airflow values from the factory and may not be as accurate as you think. I believe you are incorrect in assuming that changing the VE table will make the engine run rich when you are commanding 14.6. Normally, if you are commanding 14.6, you are (by your previous admission) in closed-loop (non-PE) and fueling is controlled by O2 sensor readings, LTFT, and STFT (and those pesky pv=nRT calculations).

    They are not accurate, that is why I wrote that it is an arbitrary number. All the things you wrote change the fueling too. So how can VE not be arbitrary. how can a naturally aspirated engine have a volumetric efficiency higher than 100%, but our tables have it. VE is just a guide of where to start the AFR. If we didn't have all th other controls (LTFT,STFT, etc) increasing VE would add extra fuel and reduce the afr. I think you can still change the aft by changing VE, but it's not going to go from 14.7 to 12. Maybe 14.7 to 14.5. It would be best if we could just get to this value on a table like we can do with PE afr.

  9. #29
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    A naturally aspirated engine can have a VE over 100% and it's possible but not likely that a modern production might actually do that over a very narrow RPM band. The VE table tell the ECM how much air is entering each cylinder given the current operating conditions of the engine. That information and the fuell pressure and injector tables allow the ECM to calculate the injector open time for the AFR it's currently trying for.

    A MAF allows an engine with a messed up VE table to still run decent as the ECM will normally prefer the MAF numbers over the VE numbers. A SD engine is much more dependent upon the accuracy of the VE table as it only has that one way to figure out the amount of air entering the engine.

    One the VE table on a SD engine is correct you should be able to use PE and other fuel tables to define the AFR you're looking for and the ECm should be able to figure out how to do it.

    Using the VE table to set AFR will work, but long term you're tune won't make a lot of sense because you'll be asking for one AFR and getting another.

    Ira

  10. #30
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    Wow guys, guess I have some reading to do later this week when I have an hour or so to digest this thread... My PCM4Less tune has very little knock retard IIRC (its been a while since Ive logged KR), but I will check it soon and try and get back.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, starting the mods
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

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