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Old 08-12-2012, 07:17 PM   #1
SouthernWRX
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Default 5th gear cruising & feedback knock

So I've been live logging here and there and I noticed some 5th gear feedback knock while cruising. I data logged some cruising earlier and am curious what could be causing this. It's all at constant speed, very little throttle/rpm/speed change. This is the the OTS 93 octane Cobb map, only other mod is an Nameless Axleback Muffler Delete. It does have some drone, could this be part of the problem? Take a look and give me yall' thoughts. Thanks.

By the way, my 3rd gear WOT logs have no FBK & very little FKL (.35 - 1.4) at the end of my runs, probably from throttle lift.

https://docs.google.com/spreadsheet/...nZ25HdGc#gid=0

Sorry for a longer log, just wanted to get some good data. This was over about a 5 - 10 mile ride.
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Old 08-12-2012, 11:00 PM   #2
AuthenticAMD
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Low load knock isn't a problem imo. Although, you had a single knock where it was at 1.99 load.
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Old 08-13-2012, 09:02 AM   #3
SouthernWRX
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Thanks for the response. So I see there at the begining of my log I have a couple counts of single knock at 1.99 and above load. Why is knock above this level bad? What exactly is calculated load? Also, why did my calculated load go from 2.03 to 8 to 1.88 (row 724-726)? Thanks.
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Old 08-13-2012, 01:52 PM   #4
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You had 1 count of knock at 1.99. The ECU drops the count by 0.35 until it gets to zero as long as there is no more knock (which there wasn't). There is no clear load where you should avoid knock, but my personal limit is 1.5 or above is something to look into. Knock is bad because as load increases, the higher the pressure in the cylinders. When it knocks under high load, there is a sharp spike in pressure under already high pressure, which could break things such as ringlands.

Calculated load is just that, a calculated load from the MAF (g/s) and Rev (R/m).

114.72 g/s
3446 rev/m = 57.433333333333333333333333333333 rev/s
(114.72 g/s) / (57.433333333333333333333333333333 rev/s) = ~1.99 g/rev


As for the 8 in the calculated load, I think that was just a glitch or something...
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Old 08-13-2012, 02:05 PM   #5
SouthernWRX
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Ok, bare with me. Just so I understand this, the first/only knock event -1.4 (row 720) happened at a calculated load of 1.99. So the other two (-1.4 row 721 - 722) and all others getting lower in number, were not an actual knock event? If this is true why did it still read -1.4 for the two cells after the initial event? Sorry for all the questions, just trying to get a better grasp on this. Thanks for the help!!!
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Old 08-13-2012, 02:09 PM   #6
AuthenticAMD
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The ECU slowly decreases the value over a period of time, so it's not an immediate reduction. If there was another knock event when it was -1.4, it would probably be -2.8. Although, I believe this value is adjustable by the tuner depending on the RPM or load.
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Old 08-13-2012, 02:11 PM   #7
AuthenticAMD
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Correct, the other numbers getting lower are not knock events.
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Old 08-13-2012, 02:17 PM   #8
SouthernWRX
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Ok, so here is another question. Why was there no FKL for the knock event? Also you mentioned in your first post "low load", what exactly is considered "low load", 1.75 or under, 1.50 or under, 1.8956231478 or under..lol? Once agian thanks.
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Old 08-13-2012, 03:32 PM   #9
AuthenticAMD
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I was trying to avoid this, but this is a good technical read on Subaru's knock control implementation.

http://www.romraider.com/forum/topic1840.html

Low load is what you're comfortable with Mine personal standard is 1.5 or lower, but some people are more comfortable with a lower number. Generally the knock sensor is more accurate at higher loads, so that means low load knock may be perceived knock but not actual knock.
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