Desired Airflow: Warm vs Cold Weather Start Compromises

[Supercharged111]

Rather than RAFIG or RAFPN, I decided to log g/s at an idle from a cold start. As I watched it all unfold, I noticed a discrepancy in the colder stuff, it seemed to be excessively high and it still does. I need to log a 0 degree or even colder start to begin to characterize to what extent. I'll do a P/N cold start idle to 180 degrees tomorrow and see what I find. Oil temp and thus the drag from colder oil is what I suspect to be a part of this, but its effect on say, 40 degrees F ECT, is more pronounced if you started around 0 ambient than 30 ambient. It seems to me a compromise would be in order here for the colder stuff, and then set the operational temperatures for where they'll be once the oil stabilizes in temperature. I'm guessing it's better to have idle airflows trim down than up? FWIW I'm not chasing a problem here, just making sure the desired airflow tables are where they ought to be. Attached is the log, it looks like frame 125 is where I remembered to put it into gear. It dipped quite a bit there, so maybe there is some tweaking I need to do here.

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[Highlander]

Not entirely sure what the "issue" is. You have 14g/s when cold and if everything lines up then you can have that as a base for your idle airflow tables.

[Supercharged111]

At first, the issue was crappy cold starts. That ended up being A0008 which I addressed prior to taking these logs. My concern was that I'd jump in and make too big of changes right off the bat. I wondered if a colder start would result in different values in warmer cells as the engine progressed to operating temperature. Below is a pic of a 36 degree start on the left, a 27 degree start in the middle, and an 18 degree start on the right.

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I'd like to get a single digit cold start to go along with all of this, I may only get one or 2 chances all winter. There is definitely a difference the colder the engine starts, but it's not huge. I think it's safe to trim some desired airflow from the colder cells. Another thing I was wondering about is if, since there's a range of airflow in any given coolant value, it's better to fudge it to the high end or the low end.

EDIT: Here's that same pic with the desired airflow table from my current tune.

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Another thing that comes to mind is does having a value here that's too high give you a flare up of RPM on initial start?

[statesman]

Oil temp and thus the drag from colder oil is what I suspect to be a part of this,

Wrong.


but its effect on say, 40 degrees F ECT, is more pronounced if you started around 0 ambient than 30 ambient.

Ahhh, now there's your problem... IAT.

GM knew that they had a problem with heat soak in the IAT sensor, so they 'bent' the airflow calculations to reduce the heat soak effect. The result is that you'll never have perfect airflow calculations because the calculated airflow always changes when the IAT changes.

Best you can do is to set your desired airflow half way between your coldest and hotest IAT, and let idle trims take care of the rest.

[Supercharged111]

Those fuckers. Thank you for weighing in, I figured I was missing something.