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Thread: Adjusting Specific BLM 'Cell' Value(s) for 165 / $6E BIN

  1. #1
    Fuel Injected!
    Join Date
    Nov 2013

    Adjusting Specific BLM 'Cell' Value(s) for 165 / $6E BIN

    Getting into the nitty-gritty of tuning my 85' Suburban with a ZZ3 crate engine running (MAF) TPI.
    The INT / BLMs seem pretty decent most of the time but the one area that I need to 'tweak' is at idle.
    Sitting at idle (BLM Cell 0) my BLMs will climb to over 150 while the INT stays around 130.
    Sounds like I need to fatten up the fuel a bit at idle?

    Anyway, I've been pouring over various threads but I can't seem to find the answer to my specific question:
    What tables / fields / scalars in the $6E BIN specifically address the values of a specific BLM Cell?
    MAF Scalar Tables?
    MAF Volts vs Grams/sec Tables?
    BLM Cell RPM Boundary?
    BLM Cell Airflow Boundary?
    Some of the above?
    None of the above?

    I apologize if I'm missing the obvious-
    I have often been accused of over thinking things
    Any advice would be most appreciated.

  2. #2
    Fuel Injected! steveo's Avatar
    Join Date
    Aug 2013
    you can't, in most ECMS, tune afr in a particular BLM cell. the blm cells are very low resolution overlay of trims over a higher resolution fueling table. what you generally do is tune AFR for the related airflow or ve value that falls within that BLM boundary. find what airflow you are actually idling at with a log and tune that in the maf table or whatever.

    if your mask has open loop idle ability, i find best results if you just forget closed loop for idle and tune your idle by feel (increase fuel to achieve max vacuum works very well). i have yet to meet an engine that actually idles better at stoich than some arbitrary richer value. most smallblock-like engines start to run smoother and cooler at like 14:1 or so.. you can't get that in closed loop.

    here's the kicker, exhaust gasses move so friggn slow at idle, it's super common to have an o2 configuration misread at idle. blms become less accurate at lower airflows, especially the more hopped up your engine. lets say your o2 sensor configuration just sucks at idle. maybe closed loop is actually adding a bunch of fuel, and your idle is now rich. don't just go adding a bunch more fuel to it... if the idle feels really good, perhaps it's ending up with a good afr. do an idle plug chop so you know where you really are, don't just go and tune based on that trim of 150+...

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