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Old 03-21-2016, 07:40 PM   #11
Scooby Specialist
Member#: 129681
Join Date: Oct 2006
Chapter/Region: MAIC
2024 Crosstrek Ltd
Ice Silver Metallic


Originally Posted by anjuna View Post
AFR will always look good out of boost. It's in closed loop, so it's hitting the target.

You won't see MAF V correction - that's not a thing.

You'll want to monitor your A/F Correction and Learning related parameters. These will show how much the ECU is changing the amount of fuel injected from what the tune is telling it, to what the actual amount of fuel is required.

The tune does it's calculations based off the MAF. The MAF says "hey, there's this much air coming in" and the ECU says "okay, let me look up how much fuel I should inject. Here we go!" and then the oxygen sensor comes back and says "hey bro, you're like, 9% lean" so the ECU says "well then I should add 9% fuel" and that's where your A/F correction comes from.

A/F learning is like a trust issue between the MAF and the ECU. It's getting tired of hearing that it's wrong from the oxygen sensor, so it learns to just ALWAYS add X percent (which is an average value over time). So then, it's just taking the MAF value, adding or subtracting the learned value, and then making closed loop corrections after that from the oxygen sensor.
You would make a great teacher. ^^^

I'll add...

And you "hope," unless you have properly determined it, that that global AFR Learning correction is correct... unless you KNOW by having tuned your ENTIRE MAF Calibration curve... the that learned value is on your side. If that correction provides more fuel than necessary... it's not so bad, only your power will suffer. But if the correction is negative, and the global correction removes fuel... because your MAF Cal at some point in open loop is off in a negative direction, by even a small amount... that's when the engine will suffer. Repeated long enough and pistons and ringlands will let you know how much.

The point is, tuning... including the MAF Cal, is important to the long-term reliability of your engine. OTS tunes are NOT so calibrated. Cheap tuners with cheap tunes don't provide it either. Get it done right, or ... roll the dice.

If it were as simple as ABC... there would be no problem, no need for TUNING. All you would need is to list your mods and get a cookie cutter tune that was perfect. But everyone knows that has gone through a tuning process that that is not the way it is. Why then believe your intake is immune to that reality.

If you keep it simple, and stay inside the envelope with a modest tune like a stage1, you can usually get away with it. But when you go higher, not so much.
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