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Old 05-06-2013, 04:11 PM   #1
snobrder540
Scooby Newbie
 
Member#: 319612
Join Date: May 2012
Chapter/Region: Tri-State
Location: Philly!!
Vehicle:
2008 WRX
DGM

Default Knock???

I'm a noob at this so please keep that in mind.

I have been watching the knock sum on the AP just out of curiosity and it will get as high as ~37 and reset back to 0 and start counting up again. I am not sure if this is a problem or not. The car accelerates and boosts just as expected.

Background:
2008 WRX
AEM intake
Cobb Highflow downpipe
Magnaflow Exhaust
Cobb 93 octane AEM stage 2 tune

I recently started watching the knock sum on my 08 wrx. It seems based on watching this that I may be knocking. I did several (4) 3rd gear pulls with data logging and all of the pulls had a 0 the whole way through on the feedback knock and the fine knock learn. Based on the ask cobb video on data logging all the data seems right where it should be but I still see the knock sum increase and I'm not sure what to make of it. Is there a problem?? please help.

Also, I'm interested in having a custom tune done. Who do you know that is good at e-tuning?

Thanks NASIOC!!!
Eric
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Old 05-06-2013, 05:00 PM   #2
endrswrd
Scooby Specialist
 
Member#: 323908
Join Date: Jun 2012
Chapter/Region: MWSOC
Location: Dayton Ohio
Vehicle:
2013 BRZ ltd
ISM

Default

Knock sums are certainly a harder topic to discuss. AFAIK an increment in knock sum is a perceived knock event, but there are other conditions that must be met for Feedback knock and Fine learn knock to occur that may not line up with what is happening during a knock sum increment. The key here is that you arent seeing any Feedback knock during pulls. This is good! But know that your knock sums will always be going up, but that doesnt necessarily mean bad things.

Those with EVOs or any experience with EVO tuning uses their Knock sum counter logic and knows that it should stay under a certain amount during(as it will reset a few seconds later). Its a similar idea, but in their ECU the knock counter is a real time counter where as, in our ECU the knock sum counter is over the entire key/power cycle AFAIK.
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Old 05-07-2013, 10:41 AM   #3
Cobb Tuning
NASIOC Vendor
 
Member#: 4803
Join Date: Mar 2001
Location: Austin, DFW, Portland, SOCAL
Default

Quote:
Originally Posted by snobrder540 View Post
I'm a noob at this so please keep that in mind.

I have been watching the knock sum on the AP just out of curiosity and it will get as high as ~37 and reset back to 0 and start counting up again. I am not sure if this is a problem or not. The car accelerates and boosts just as expected.

Background:
2008 WRX
AEM intake
Cobb Highflow downpipe
Magnaflow Exhaust
Cobb 93 octane AEM stage 2 tune

I recently started watching the knock sum on my 08 wrx. It seems based on watching this that I may be knocking. I did several (4) 3rd gear pulls with data logging and all of the pulls had a 0 the whole way through on the feedback knock and the fine knock learn. Based on the ask cobb video on data logging all the data seems right where it should be but I still see the knock sum increase and I'm not sure what to make of it. Is there a problem?? please help.

Also, I'm interested in having a custom tune done. Who do you know that is good at e-tuning?

Thanks NASIOC!!!
Eric
Hi Eric. The knock sum value itself does not have any meaning. This is because it is incremented even when the ECU would ignore those knock events, such as at idle. This is because the Subaru knock detection system cannot distinguish between knock and other engine noise at very low load. The only use that knock sum has is to check for perceived knock events at higher load when the system is more accurate. In that case, you would look at when knock sum increments, which would be a perceived knock event by the ECU. This can be useful when you are seeing some fine knock learning being applied as fine knock learning can be applied over and over after the original event (until it ramps back to zero), so it can be a little more difficult to determine when a current knock event occurring. Keep in mind that even at higher load, you will see some false knock, such as with throttle changes, especially larger throttle changes.

Bill
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Old 05-07-2013, 04:49 PM   #4
snobrder540
Scooby Newbie
 
Member#: 319612
Join Date: May 2012
Chapter/Region: Tri-State
Location: Philly!!
Vehicle:
2008 WRX
DGM

Default

Ceir Thanks! I'll be in touch.

Thanks Bill that is very reassuring.
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