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Thread: Running lean when cold

  1. #1
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    Running lean when cold

    Hey guys, just like every other fall/winter since my build was finished I'm having issues running too lean when ambient temp is below 50 degrees F or so. Engine is a 350 bored out to 357 with bored out throttle body, summit vortec heads, edelbrock vortec carb intake with adapter to convert to tbi running factory air cleaner. I've added in an IAT sensor on the air cleaner and enabled the MAT in the bin. Have maxed out the "TPS difference AE correction factor vs. MAT" from 20 degrees C and lower to 2. I've tried changing "MAT & CTS Blend Multiplier vs. Airflow" to everything from a stock CPI .bin to everywhere from .100 to .800 in that table. Doesn't seem to be any difference whether engine is in open loop or closed loop, IAT reads the correct temperature. I'm pretty perplexed at this point and I'm hoping someone that knows a lot more about this than I do can tell me what I'm doing wrong. I can pull over and let the engine heat soak at idle for about 5 minutes and my afr's will be back to normal, it's like no matter what I adjust in the .bin the ECU just doesn't compensate for the colder air coming in, or at least doesn't compensate enough.

  2. #2
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    I can pull over and let the engine heat soak at idle for about 5 minutes and my afr's will be back to normal
    Are you referring to the displayed AFR in scan data? Are you using BLM / INT to determine AFR's are not where you would expect them to be?

    Doesn't seem to be any difference whether engine is in open loop or closed loop
    Please explain this better. In open loop desired AFR is obtained from a table. How far does displayed AFR vary from desire AFR in open loop?

    Regardless of the numbers, how is the vehicle running when this occurs?

  3. #3
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    No sorry my AFR displayed on my AEM wideband that I am datalogging in Tunerpro.

    What I meant by open loop or closed loop is that I was running open loop while doing the initial tuning and getting the actual AFR vs desired AFR to no more than 5% average deviation during a datalog I had this issue, and now that I have put it back in closed loop after getting the VE table set right, the issue still happens.

    My BLM/INT and actual AFR via the AEM wideband are perfect as long as ambient temperature is above 55F or so, or if I'm in stop and go traffic where the engine can heat soak when it's colder outside. It also isn't a straight dive off a cliff, I can see my AFR creep up a couple points during AE as the ambient temperature goes down but once it's around 50-55F outside the engine really starts to get a lean stumble because there's not enough AE and I start to notice it actually accelerate poorly. What is happening is the AE isn't enough when cold outside. If I add AE so it's good when it's cold, it's too much when it's hotter outside. I added the IAT to help with this, but it is not making any changes to my AE when the ambient temp is cold, or at least not enough. I had found a couple threads on here with similar issues and adding an IAT fixed the problem immediately but it made no difference on my issue.

    Basically what happens when looking at the logs is I'll accelerate mildly (enough for AE but no enough to get into PE) and the AE that is normally perfect isn't enough with the colder air and I get a lean spike before the o2 reacts and drives the int/blm up and adds fuel but it's already too late. I know it's an issue with the AE when it's cold outside I just can't for the life of me figure out why adding the IAT and enabling it and setting the blend table for it as others have hasn't helped at all on my truck.
    Last edited by 95GMC; 09-26-2022 at 05:36 PM.

  4. #4
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    So I guess nobody has seen this issue before where the MAT is enabled but doesn't add the extra TPS AE at lower temps?
    Last edited by 95GMC; 09-29-2022 at 12:39 AM.

  5. #5
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    Quote Originally Posted by 95GMC View Post
    So I guess nobody has seen this issue before where the MAT is enabled but doesn't add the extra TPS AE at lower temps?
    It has been a long time since I messed with this. From memory need to increase the IATs contribution where you are having the issue as well as increase the AE multiplier in that area. I will try to remember to look at the actual PCM code when I get time to.

  6. #6
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    Quote Originally Posted by Fast355 View Post
    It has been a long time since I messed with this. From memory need to increase the IATs contribution where you are having the issue as well as increase the AE multiplier in that area. I will try to remember to look at the actual PCM code when I get time to.
    Thanks this is where I have my tables set right now vs a stock BPLH bin:

    My current settings

    MAT 1.PNG

    Stock BPLH

    MAT 2.PNG

    I'm curious if there's a table or something that needs to be populated with something besides 0 to enable the MAT/IAT input that I'm missing. I have MAT enabled and those 2 tables populated which is all I read about people doing in other threads so I'm not sure. I even went as far as using another PC, chip burner, ECU, XDF file and updating Tunerpro to eliminate any variables but I just can't seem to get the extra AE when it starts to get colder out no matter how drastic the changes I make are.

    One other thing I hope I'm not wrong on is the left column on the AE correction factor table, it has a capital C so I assume it's Celcius but if it was actually supposed to be Fahrenheit that might explain my issues.
    Last edited by 95GMC; 09-29-2022 at 03:08 AM.

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