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Old 08-09-2012, 10:11 AM   #1
SouthernWRX
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Member#: 321571
Join Date: May 2012
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2012 WRX Base
Ice Silver

Default Data logging "Why' Questions.

So I'm a complete newbie when it comes to the AP, however I am now obsessed with this darn thing and the logging feature. Unfortunately the more I look into it and read, the more I confuse myself. so...

Why do we data log in 3rd gear from 2K to around redline?

Why not from a dead stop all the way through 3rd?

From my understanding "Knock" is the same thing as detonation, correct? Also from what I understand, when a knock event occurs it cause fine knock learning (FKL), which is also no good, correct? However there is such a thing as "false knock", but this still causes FKL, correct? So if false knock is nothing more than under hood noise and not causing harm, is the FKL event that is triggered by this false knock causing harm?

In a perfect word I assume you would never see any knock at all, but nothing is perfect. I've been live logging and data logging all this week and Ill get one count of knock just out of nowhere. I'll be cruising at a constant speed and, BAM, feedback knock -2.8 for one cell in my spreadsheet. So I think to myself, "what caused this? was it harmful? is this normal?"

Sorry for the long post and I have been searching the forum and internet to educate myself. Unfortunately I believe I have over stimulated my brain and am confused . Any comments will be greatly appreciated and any reading material yall think may be beneficial would be great as well. Internet, books, magazines, papers...whatever. I just want to have a good grasp on this.

Thanks.
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Old 08-09-2012, 03:43 PM   #2
Cobb Tuning
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Quote:
Originally Posted by SouthernWRX View Post
So I'm a complete newbie when it comes to the AP, however I am now obsessed with this darn thing and the logging feature. Unfortunately the more I look into it and read, the more I confuse myself. so...

Why do we data log in 3rd gear from 2K to around redline?

Why not from a dead stop all the way through 3rd?

From my understanding "Knock" is the same thing as detonation, correct? Also from what I understand, when a knock event occurs it cause fine knock learning (FKL), which is also no good, correct? However there is such a thing as "false knock", but this still causes FKL, correct? So if false knock is nothing more than under hood noise and not causing harm, is the FKL event that is triggered by this false knock causing harm?

In a perfect word I assume you would never see any knock at all, but nothing is perfect. I've been live logging and data logging all this week and Ill get one count of knock just out of nowhere. I'll be cruising at a constant speed and, BAM, feedback knock -2.8 for one cell in my spreadsheet. So I think to myself, "what caused this? was it harmful? is this normal?"

Sorry for the long post and I have been searching the forum and internet to educate myself. Unfortunately I believe I have over stimulated my brain and am confused . Any comments will be greatly appreciated and any reading material yall think may be beneficial would be great as well. Internet, books, magazines, papers...whatever. I just want to have a good grasp on this.

Thanks.
3rd gear works because you want an extended run from lower RPM to high where you will hit your peak boost target and also not too fast as to make it unsafe to get the actual log. You will not likely hit your peak target in lower gears (definitely not in 1st). A 3rd gear run from about 2000 RPM on up will put the car under heavy load for a good period of time so you can see how the car reacts. It is a consistent run that you can generally safely do on the roads and use to compare different logs.

Subaru's knock control system is a compromise between effectiveness and cost. As such, it isn't always accurate at determining a knock event. The engineers know that and understand that there will be some false knock reported and responded to by the ECU, especially at low load/RPM and during throttle transients. A lot of this is just noise. Actual knock, even severe, is quickly responded to by the ECU pulling timing and it has quite a bit of authority to do so. If the ECU responds to false knock, it is not going to cause a problem due to the correction.

It can be a bit tricky to determine false knock from actual knock, but if you are seeing knock events (feedback knock correction or fine knock learning) in the middle of your WOT run consistently (and not when you are mashing the throttle or lifting off the throttle), then that is more of a concern than anything else. Fine knock learning is a little tricky as it learns based on an event and then is applied over and over again to a range of load and RPM surrounding where the event occurred. So, just because you see fine knock learning doesn't mean it was learned right then. Some ECUs have the knock sum parameter - you can add that to your logs and look at when it increments - that will tell you clearly that a knock event has occurred. Don't worry about the knock sum value(s) by itself - just when it increments. But, keep in mind, that any of these cars whether they are stock, modified and regardless of the tune, will have the occasional reported knock, especially at low load/RPM and during transients.

Bill
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Old 08-09-2012, 05:31 PM   #3
SouthernWRX
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Member#: 321571
Join Date: May 2012
Chapter/Region: TXIC
Location: Cypress, TX
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2012 WRX Base
Ice Silver

Default

Bill,

Thanks for the response. This clears up alot of my concerns/questions. I do however have two more questions. If I'm logging the knock sum value and see a knock event, however no change in my sum value, is that false knock? Also, why is it I sometimes I'll see a knock event (single count, 2 - 6 cells worth) but no FKL? Once agian thanks for your time and help.
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Old 08-10-2012, 09:58 AM   #4
Cobb Tuning
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Originally Posted by SouthernWRX View Post
Bill,

Thanks for the response. This clears up alot of my concerns/questions. I do however have two more questions. If I'm logging the knock sum value and see a knock event, however no change in my sum value, is that false knock? Also, why is it I sometimes I'll see a knock event (single count, 2 - 6 cells worth) but no FKL? Once agian thanks for your time and help.
If any of the knock sum values do not increment and you see fine knock learning, that means those corrections were learned from a prior perceived event. When feedback knock correction drops from the previous value, that is a knock event and you should see one of the knock sums increment as a result (feedback correction will start to ramp back to zero pretty much immediately if there is no additional knock - those negative values are not knock but just the ramping behavior). If the DAM drops (other than after a map reflash or ECU reset), that is also a knock event and should show up an incrementing knock sum. If knock sum increments but there is no feedback/fine/DAM correction, then that means the ECU has ignored that perceived knock event (likely at low load/RPM).

Bill
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