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Old 01-24-2008, 05:46 PM   #1
Tea cups
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Default Subaru's Knock Control Explained

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Last edited by Tea cups; 10-13-2008 at 11:10 AM.
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Old 01-24-2008, 05:46 PM   #2
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see link above

Last edited by Tea cups; 10-13-2008 at 11:10 AM.
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Old 01-24-2008, 05:48 PM   #3
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This is the sticky that was on the Enginuity site before it went down. I've also updated it with an explanation of FBKC disable as well as various sections for clarity.
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Old 01-25-2008, 08:12 PM   #4
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This should be stickied here as well! Thanks for putting this up here in Enginuity's absence!
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Old 01-25-2008, 10:01 PM   #5
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Saved to my own docs thanks!
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Old 10-08-2008, 06:04 PM   #6
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This is a good explanation for knock control, one question I was hoping to answer is a rather basic one: Where is the stock knock sensor on my car* and how does one tap into the output from it, or log the output to monitor knocking?

*My car is an 04 WRX but I'm sure other model owners would have the same question.
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Old 10-08-2008, 06:41 PM   #7
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Old 08-03-2010, 11:16 AM   #8
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Tea Cups Im hoping you still browse Nasioc...

How would one go about disabling rough correction? I would my timing to always pull from the base table, Fine correction can still run but i would only like it reducing by a max of -2 degrees. i have a 32 bit ecu

thanks
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Old 08-04-2010, 01:49 AM   #9
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Each knock correction mechanism has a min and max RPM where it is enabled, and a min/max load as well. If you set your rough correction min RPM to 10,000 you'd never get rough correction.

You could also change your advance table so the largest value is, for example, 4 degrees. Then you'll never lose more than 4 degrees to rough correction. And if you look at the tables in the knock correction group you'll find a couple more ways to effectively disable rough correction.

However this all sounds like a bad idea. I have effectively disabled rough correction by getting my timing and AFR set up so that the engine rarely knocks. I recommend this approach to everyone.
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Old 08-04-2010, 08:52 AM   #10
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Well I always run goods fuel and there are other tables to prevent knock when the temperature starts to rise. I moved the load and rpm out of bounds, set max retard and step to 0

Yeah thats what i had in mind i just wrote a PDF on my actions if someone wants to have a gander at it.

It's just on the dyno when we were logging the factory knock sensor must be marginally to sensitive on cruise. just watching the knock counter go up. So either false knock or a sensitive sensor will pull the IAM down on cruise to a point were it runs the WG spring pressure. We had knockbox on the motor and it wasnt detonating or showing predetonation signs.
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Old 08-05-2010, 03:20 AM   #11
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Ahhh, context is everything. I like that idea. I suggest disabling fine correction as well - just leave feedback knock correction active, and as long as you only make small changes between dyno runs you'll still have all the correction you need.

Studying logs and reflashing after every pull is basically a knock correction method unto itself, and your judgment is probably better than the ECU's anyway.

The more I think about this, the more I like it. I will ponder it some more, but I think I'm going to start doing this to my ROMs while I'm logging pulls on the road, and then re-enable IAM and FLKC when I'm done logging. I don't get the sort of cruise knock you're talking about, but when I do get a knock event during a pull, I always repeat the pull a couple more times to see if it was legit or just noise. This would spare me the trouble of resetting the ECU to clear the FLKC table, and dealing with the hunting idle that always follows a reset. And at least once (that I know of...) I've done a logging session and found out afterward that I had a knock event while the logger wasn't running, which put a correction into the FLKC table, thereby invalidating some of my logs.
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Old 08-05-2010, 04:42 AM   #12
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Im also wondering as an additional map Hopefully romraider guys are reading, would be a knock sensitivity table so you can set what voltage is knock...

Yeah well my car at the moment is quite inconsistent and it always takes a decent amount of driving to get the iam counter and fine correction back up and it's a little annoying. and my issues seems to be noise on cruise and when you do a pull the ecu's still got everything wrapped in bubble wrap. After each flash its perfect when the IAM is set to 50% and the fine correction and rough correction is all reset.

Thinking about it now just having the knock correction it might pull 1-2 degrees on cruise which from 35degrees is really only going to effect minor long term efficentcy. As soon as the motor is opened up and the noise is gone its back to the base map timing as tuned, If you happen to get any real detonation then it will pull it back only once.

And yes given that i've viewed logs, put good fuel in it would be a unicorn event for knock so having a once off knock control should suffice.

Will be implementing and testing over the next few weeks
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Old 08-05-2010, 05:35 AM   #13
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I'm not sure if I understood that 3rd paragraph, but just in case... Feedback knock correction will pull lots of timing if it has to. Something like 2 degrees per knock event, up to a max of 12 (both numbers configurable in the tune).

There have been a few threads from people with mystery cruise knock, not many end with a solution. One guy did find that his knock sensor was defective though.

See also:
http://forums.nasioc.com/forums/show...0#post31109660
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Old 08-06-2010, 11:59 AM   #14
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Well i know i have a clutch plate rattle on cruise not sure how transparent that is but it could be related.

New target i have a max retard of 2 degrees .3 degrees each event.

2 degrees off high load cell timing range of 2-16 degrees should be plenty. Would have to be some nasty fuel/ clogged injectors/ or extreme heat to get past that.

Ill have to log it and see how quickly it pulls timing and adds it back.

the timer is 125, im hoping that ms?

if so from cruise the car might be doing 2400, ecu sees a few false knock events and maxes out feedback correction at -2 degrees. as soon as it becomes clean when car is back at wot, 800-1000ms may have gone by should see all the timing back in which depending on gear ect ect might be 4000rpm.

so this strategy would effect driving the least unlike a IAM . Which if on cruise for long time iam drops below 10%> its running no boost control and on a fail safe map and has to run through a heap of loops> seeveral WOT pulls before it and the fine correction are back in the fun zone


Makes sence to me?? Should be worth a test do you think?
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Old 08-06-2010, 01:54 PM   #15
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I'm inclined to completely disable IAM and FLKC, and set FBKC for 1 degree of retard with a max of 3 or 4. Feedback knock correction tapers back to zero pretty quickly, so unless you max it out right at the start of the pull, it will be gone for most or all of the pull. That way if you do get legitimate knock during the pull, the ECU will be able to correct for it.

If you disable IAM and FLKC, then you only need to log FBKC to know exactly what's going on. I really like this idea.

I don't know what the timer units are. I wouldn't be surprised if it was crankshaft rotations, though.
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Old 08-10-2010, 05:33 AM   #16
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ive done some logging today and it's what i imagined. The clutch is rattling on cruise/ light throttle and at idle just blipping throttle. To make sure it was detonating i make appropriate adjustments and the noise was exactly the same.

Now after you go over the same fine learning cells you can end up running -5 degrees total timing from a base of 20-30+

On cruise and between shifts there were also instances of rattle only enough to tally -1.5 FBKC at 2500 and that took until 4.5K to end up back at 0.

I then done a similar plan to above and put everything on a tight leash, max fine correction and FBKC to -2 degrees each, i also shortented the delay. To fix the idle rattle i lifted the range from 1200 to 2000 so it ignores it.

The car is running alot more consistent already.

More logging to come.

Would be interesting to explian to exedy and other clutch users that rattling springs in a clutch disk can affect performance in a big way!
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Old 08-10-2010, 05:57 AM   #17
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Interesting. Which model of clutch do you have?
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Old 08-10-2010, 10:28 AM   #18
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it was a modified pressure plate and exedy clutch disk, Quite a few people in aust with the same problem with the springs in the clutch disks. On the romraider forums there was a couple of users who also mentioned increased noise under 2000rpm which i thought was interesting.

After more driving the fine correction tables are looking good now i have changed the load and rpm limits to ignore light throttle and gear changes

Additionally if you change your iam to 100% and the step value to 0 which id imagine some tuners would do for consistent tuning you need to ensure on the 06 ecu's atleast that you reset the ecu in the learning view software. Until this is done the ecu wont use the new initial value and since the step value is at 0 it wont change.
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Old 08-31-2010, 12:43 PM   #19
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Any further progress on disabling IAM and FLKC to create a FBKC only (UTEC-like) control system, NSFW?
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Old 08-31-2010, 11:54 PM   #20
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No, I killed my clutch a couple weeks ago so my car has been down. It should be really easy though, just set the minimum RPM for FLKC and IAM to 10,000 or so.
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Old 09-01-2010, 01:40 AM   #21
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Just did it today, it's certainly a bit easier to only watch FBKC and get a relatively stable value with no other compensations in the mix while tuning.
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