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Thread: Does the E38 reference the Stoic AFR table, non-flex fuel equipted?

  1. #21
    Advanced Tuner
    Join Date
    Aug 2011
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    Alaska
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    Mike –

    Once again, I DO appreciate your time. It’s soooo difficult learning this stuff without a logic diagram. I much prefer to understand the theory of operation and what / how a machine or device works than to be simply told how to do something. So your attempts to educate are helpful.

    Sorry about the E85 statement. Not sure what I was thinking, but I meant E10. And no, our fuel is straight gasoline. A friend of mine is the fuel distribution manager for the area, and he ensured me that the gasoline he supplies the gas stations in this area does not have any alcohol. He gets it straight from the refineries. They do not blend it with anything but brand specific additives.

    The manner in which the O2’s work, and how you are explaining it is how I have always understood it. They are nothing but lambda sensors and report mV to the ecm that represents lambda and how far away from lambda the exhaust mixture is. It is this Stoic AFR setting and what the ecm does with it that has me curious. Dave said the ecm references this figure. Iam Broke said the same thing. The other tuner I mentioned in the OP said the same thing. I know some other tuners change this from the OEM settings to something lower, even if their customers use straight fuel, which should be 14.7 stoic. I figured that I would ask the question to here, so find out for certain.

    My logs over the past few days are indicating that fueling has changes after I moved the stoic AFR setting to 14.2 from stock (14.7). And it isn’t just open loop, but closed as well. The change in average LTFT’s I noted above were after long drives and the ecm was in closed loop the vast majority of the time. I did my best to avoid rapid throttle changes and to keep steady rpms in several MAP areas. The LTFT averages are consistently showing about a - 3% difference between the 14.7 and 14.2 stoic afr setting change that I made (-3%). I took two other long drives yesterday and logged them both. One drive was with MAF disabled, the other with SD disabled. I also disabled CFCO and DFCO and PE as well. I wanted to see if either MAF or SD fueling was off more than the other. Both are still quite close and I did not find any areas of either the VE table or MAF table that were off more than 3%. They were both still close enough to not bother re-calibrating either. I also logged commanded AFR, and commanded EQ ratio. AFR is a steady 14.2 and EQ is a steady 1.0.

    It will be several days before I can experiment further. I intend to install the WB and do some more tests, but not sure exactly when I will have time to do that.
    When arguing with an idiot, make sure he isn't doing the same thing....

  2. #22
    Advanced Tuner Jabbott's Avatar
    Join Date
    Oct 2006
    Location
    Richmond
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    223
    Mike,
    I had a hard time with this also a couple of years ago. I think all of us Americans are wired for AFR. It is difficult to do away with it though when GM has listed in the ECU, but it is just a reference for EQR. EQR is what the ECU operates in all the time. Lambda is what the O2 sensors are looking at in closed loop and correcting to. If you changed your Stoich to 14.2 you may show a low trim because that really is the lambda 1 for E10 fuel. If you change your stoich to 14.7 you will not see a difference in the trim because it is still correcting to lambda 1 based off how much fuel is needed for the incoming air. Now where the stoich number is important is in all the fueling tables that use EQR, because they are referenced off of the stoich table. For example your stoich is 14.2, in your PE table you are asking for a PE EQR of 1.18, that would be 14.2/1.18 show your new AFR would be 12.05. Now GM could have made this more logical by just using lambda on everything for fueling. Your stoich would be 1.00 your PE could be .78 lambda etc. Hope this explained it for you. You just have to get used to what the ECU is using and not what would make sense.
    Last edited by Jabbott; 06-25-2013 at 11:22 PM.