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Thread: What am I missing here?

  1. #1
    Fuel Injected!
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    What am I missing here?

    I've been googling this for days and I'm just getting confused, I think a fresh set of eyes will have the answer.
    I just bought a stock 1995 4x4 GMC Yukon with 5.7 TBI/4L60E, BJYL-$0D-5.7-auto.bin.
    I've been logging it cruising at 60MPH on the motorway and the BLM's are all around the 120-121 mark and my INT values are in the 127-131 range.

    If my long term BLM's at 120 are on the rich side of things why is the short term integrator sitting right around 128?
    It doesn't look like the integrator is trying to pull the BLM's up towards 128, what am I missing here?

  2. #2
    Fuel Injected!
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    Quote Originally Posted by Kitch View Post
    I've been googling this for days and I'm just getting confused, I think a fresh set of eyes will have the answer.
    I just bought a stock 1995 4x4 GMC Yukon with 5.7 TBI/4L60E, BJYL-$0D-5.7-auto.bin.
    I've been logging it cruising at 60MPH on the motorway and the BLM's are all around the 120-121 mark and my INT values are in the 127-131 range.

    If my long term BLM's at 120 are on the rich side of things why is the short term integrator sitting right around 128?
    It doesn't look like the integrator is trying to pull the BLM's up towards 128, what am I missing here?
    The BLMs purpose is to keep the Integrator at 128. Its just like Short Term and Long Term fuel trims. The BLM will move up or down in response to changes in the Integrator. If the Integrator is near 128, the BLM has no reason to move. Looks like your tune is a little rich but not outside of what most stock vehicles run at.

  3. #3
    Fuel Injected!
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    Thanks for the reply, that makes sense.

    Based on that is this sort of how it works?:

    BLM of 120 means : 120/128=.94
    My long term fuel trim is causing 94% of the fuel calculated (in my "Open Throttle VE vs MAP vs RPM" table) to be delivered to keep the O2 sensor happy.

    In a perfect world Closed loop would see the BLM and Integrator values at 128

    So while referring to anything <128 to be "rich" in my case the engine isn't actually running rich at the moment because the Integrator has trimmed the BLM to a value where the engine is running as close to stoichiometric as the O2 sensor input could get it.

    For whatever reason initially the O2 feedback would have been telling the Integrator the BLM was 6% rich and needed to reduce the amount of fuel being supplied.
    The BLM needed to be changed to <128 to reduce the rich condition, it was basically saying you either manually reduce the values in your VE table (because the amount of fuel supplied is linked to the VE values) or I will trim the BLM to 120 to achieve the same result.

    The above sort of makes sense to me but I get confused when I've read that the Integrator is always trying to pull the BLM to 128, in my case it looks like the Integrator has pulled the BLM to 120 to maintain it's Integrator value near to 128.

    Am I right in how I think this works?
    Last edited by Kitch; 05-31-2016 at 11:24 PM.

  4. #4
    Fuel Injected!
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    Quote Originally Posted by Kitch View Post
    Thanks for the reply, that makes sense.

    Based on that is this sort of how it works?:

    BLM of 120 means : 120/128=.94
    My long term fuel trim is causing 94% of the fuel calculated (in my "Open Throttle VE vs MAP vs RPM" table) to be delivered to keep the O2 sensor happy.

    In a perfect world Closed loop would see the BLM and Integrator values at 128

    So while referring to anything <128 to be "rich" in my case the engine isn't actually running rich at the moment because the Integrator has trimmed the BLM to a value where the engine is running as close to stoichiometric as the O2 sensor input could get it.

    For whatever reason initially the O2 feedback would have been telling the Integrator the BLM was 6% rich and needed to reduce the amount of fuel being supplied.
    The BLM needed to be changed to <128 to reduce the rich condition, it was basically saying you either manually reduce the values in your VE table (because the amount of fuel supplied is linked to the VE values) or I will trim the BLM to 120 to achieve the same result.

    The above sort of makes sense to me but I get confused when I've read that the Integrator is always trying to pull the BLM to 128, in my case it looks like the Integrator has pulled the BLM to 120 to maintain it's Integrator value near to 128.

    Am I right in how I think this works?
    The Integrator drives changes in the BLM to keep the Integrator near 128. Lets say it was the other way around and you had a partially plugged fuel filter. The Integrator would increase in response to lean 02 readings. As the Integrator rises the BLM follows. Once the O2 sensor responds by getting richer the Integrator levels out at 128. BLM may be 136 at that point. You can datalog BLMs and make VE table changes accordingly.

  5. #5
    Fuel Injected!
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    Cool, finally getting an understanding of how it actually works rather than just doing it.

    So the closer I get my VE values in the "Open Throttle VE vs MAP vs RPM" table to equate to BLM values at 128 the better place to start for open loop fuel metering?
    Last edited by Kitch; 06-01-2016 at 01:21 PM.

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