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Old 03-04-2014, 12:27 PM   #12
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Originally Posted by TM View Post
This thread has a lot of great information for beginners to start to understand their data logs.

My questions is: How do I know if something is out of the ordinary? AFR too high/low? KC learned value? Advanced multiplier dropping? I'm not sure exactly how to spot trouble areas. And after we locate a problem, what needs to be changed to address that problem?
to understand what is wrong, you need to have a general understanding of what is correct. basically the two things you care about as someone logging their car (i.e. not tuning it), are fueling and timing.

for fueling you want to make sure that trims are low (<5%) and that you are hitting your afr targets. for now OFT can't log eq. ratio commanded (it's coming in the update though), so you'll have to correlate load and rpm with afr targets from the fueling map, then see in the log if you're on target. short trims will always be zero in open loop, so disregard that. any LTFT being applied in open loop is problematic and will likely cause you to miss fueling targets, and should be corrected. when it comes to fueling error, you should really employ spreadsheets or other tools for the closed loop portion, and use the log viewer to confirm that your on target in open loop.

timing is also very simple: it just shouldn't be pulling any, ever. at least that's my opinion, some people say knock correction is ok, and i argue that it's ridiculous to say that. knock correction costs you power vs. tuning up to the knock wall and backing off a bit, and it's an imperfection. we tune cars to be perfect. if perfect can be done (and it can) it should be. anything less is unacceptable to me. others feel differently.

for this you'll want to make sure that FLKC (when it's available to log via OFT) is always zero, and that FBKC is not consistent or repeatable. you'll inevitably have some FBKC here and there at low loads (particularly throttle tip-in), but the big thing is to make sure that it's not writing in to FLKC, or happening repeatably under high load. your IAM should always be 1, period. if it's not, you're losing significant power across the board, and something should be corrected.

the biggest misconception on this forum that i've found is that a low IAM is ok. i've read posts by people suggesting that your IAM 'should be closer to 1' in one scenario or another. this is insane to me. your IAM should just be 1, if it's not you have a significant problem. IAM is coarse correction. it is the ecu's last attempt to save itself. if it drops, you lose power everywhere, when in reality you probably just need to pull a degree or two from one little area somewhere in the advance table to make it happy and stay at 1. it's the ultimate 'looks good!' response in my opinion. one could argue that having it drop isn't dangerous as long as it stabilizes, but that isn't the point. it's incredibly suboptimal, in terms of the actual tune itself. the entire point of tuning is optimization. there is no need to accept this as 'normal'. it's been well accepted and understood for a long time in the subaru tuning community that an IAM less than 1 is not 'normal' or 'ok'. it's something requiring immediate attention if you want your tune to be anything close to optimal.

that's really about it from the 'is my car ok?' perspective. there's not much to it. just collect a lot of data for closed loop, and short logs for open loop. check that everything is on target and not pulling any timing, and that'll let you know that things are performing as intended and that you tune is safe.

Last edited by jamesm; 03-04-2014 at 12:38 PM.
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