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Thread: And yet another question about blm numbers.

  1. #1
    Fuel Injected!
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    And yet another question about blm numbers.

    Just out of curiosity, and I know I can focus on things a little too much, but, I've run 4 logs, 2 going to work and 2 going home.

    I see that the blm's are generally within 2-4 points of 128, but there are a few that have fewer counts, (between 5-15) that seem to vary as much as 8 points between runs.

    Is this something to be concerned with or are these numbers a result of ambient weather conditions?

  2. #2
    Super Moderator dave w's Avatar
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    I feel an average of + / - 5, (133 ~ 123), is acceptable. I would make an adjustment to VE cells that are consistently showing BLM averages of + / - 10 (less than 118 or greater than 138). The ideal average of 128 is a moving target, not easy to get consistently (in all kinds of driving / weather conditions)!

    dave w

  3. #3
    Fuel Injected!
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    The cells that are in question have had a couple logs that were less than 5 from 128, and in other runs more than.

    These cells also don't have high sample counts either which made me wonder.

    Will run a few more and see if I can figure out a trend.

  4. #4
    LT1 specialist steveo's Avatar
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    imo,

    without 40+ hits in a cell, but also some wide coverage across the entire range, the blm data is totally irrelavent, and shouldn't be adjusted, however you can use adjacent cells to determine a curvature.

    this is why you have to combine average data from a whole ton of logs with a whole bunch of different driving before it becomes usable.

    also in a cell that covers more than 1500rpm or 30 map, you can't trust it much either, since it ends up averaging on the high and low side of a curve a lot of the time, so all you can really adjust is a median value which ends up making it hard to get your fueling curve right.

    you can get around this; adjust your blm boundaries and hystersis to get a more fine grained grid in the range that you want to tune so you get more reliable data and can see how the curve is.

    my opinion is if your BLMs exceed 132 they need to be tuned, but if i find they're around 118-122 i dont even stress it, that's just 'a hair rich', and that's ok.

    this follows the old carb mentality of 'slightly rich is better than slightly lean'. i figure it's alright to start a hair richer and let closed loop lean it out for you.

    i've also found that the integrator removing fuel seems to happen more quickly/accurately than adding it, but your results may vary?

    and yes, depending on weather and a bunch of other factors, it'll never hold true. it doesnt' take much of an environmental variance to throw you off by a couple afr points, but you'd never even feel it, CL fixes small errors really quickly.

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