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Old 06-15-2011, 12:52 AM   #1
WrXtaCy2003
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05 LGT 35r 30psi..busted

Default FFS and false knock

Has any solution ever been found for this? And yes it is false knock, it only happens at the FFS point, and my car never knocks when not using it. I tried setting the feedback knock range to end at 5000rpm and the load to end at 3.0g/rev. But it still pulls mad knock at every ffs event. I used to have an AEM, so this was not an issue, and I remember hearing about this with the stock ecus. I tried searching here and google and have come up with nothing but setting the FFS rpm at 4800rpm which just stops you from bouncing off the limiter, but it sometimes causes a slight hesitation. So i was wondering if there is any fix for this. I'm OK if there is a way to just completely shut off knock control ( for track use only), but It seems I couldn't get that to work either. Thanks.

DK
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Old 06-15-2011, 09:58 AM   #2
Cobb Tuning
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Originally Posted by WrXtaCy2003 View Post
Has any solution ever been found for this? And yes it is false knock, it only happens at the FFS point, and my car never knocks when not using it. I tried setting the feedback knock range to end at 5000rpm and the load to end at 3.0g/rev. But it still pulls mad knock at every ffs event. I used to have an AEM, so this was not an issue, and I remember hearing about this with the stock ecus. I tried searching here and google and have come up with nothing but setting the FFS rpm at 4800rpm which just stops you from bouncing off the limiter, but it sometimes causes a slight hesitation. So i was wondering if there is any fix for this. I'm OK if there is a way to just completely shut off knock control ( for track use only), but It seems I couldn't get that to work either. Thanks.

DK
We haven't been able to re-create the false knock issue in-house, but it is obvious that a small number of users experience this on Subarus using the factory fuel cut limiter for FFS. There are two schools of thought on this. One is that it is real knock (when the fueling is resumed after letting out the clutch) and can be mitigated by removing timing in the low load, higher RPM area (at and above where your FFS set point is). The other is that it is false knock.

If you believe it to be false knock (and removing timing as explained above does nothing), then you need to determine which knock response is the culprit. Generally, we wouldn't recommend that anyone do this but it might be needed in a racing situation. If it is feedback knock correction, then you can modify the max. RPM range to determine when the correction is not applied. The same can be done for the fine knock learning and DAM RPM ranges. It is not necessary to modify the load range. Keep in mind that prior to our overhaul of the AccessTUNER software in Feb. of this year, there were some of the knock control ranges that were not defined (or defined incorrectly). I recommend that you update to the latest. If you have AccessTUNER Race, you can do this by re-submitting a request for the software (the new software has an auto-updater so you won't have to re-submit again for future updates).

Bill
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Old 06-15-2011, 05:21 PM   #3
WrXtaCy2003
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Thanks bill, I'll try removing some timing in that area and see what happens. But to be clear, I have my FFS at 6500 and I shift at 7000rpm. You suggest I remove timing from where the load area where FFS limiter is occurring? Since I'm at about 16psi during FFS, I should remove timing at whatever load that corresponds to, at and a little around the FFS limiter which is 6500, and then obviously smooth things out? In my logs, at the FFS point I am at 2.5g/rev at it runs about 33deg timing on the limiter. I will try removing timing and see what happens. Also, I believe I have the most current software and firmware, I just got my AP a week ago. Thanks for the quick response.

Dustin
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Old 06-15-2011, 07:40 PM   #4
Cobb Tuning
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Thanks bill, I'll try removing some timing in that area and see what happens. But to be clear, I have my FFS at 6500 and I shift at 7000rpm. You suggest I remove timing from where the load area where FFS limiter is occurring? Since I'm at about 16psi during FFS, I should remove timing at whatever load that corresponds to, at and a little around the FFS limiter which is 6500, and then obviously smooth things out? In my logs, at the FFS point I am at 2.5g/rev at it runs about 33deg timing on the limiter. I will try removing timing and see what happens. Also, I believe I have the most current software and firmware, I just got my AP a week ago. Thanks for the quick response.

Dustin
Load will rapidly drop when you push in the clutch, so the idea is to focus on those low load, high rpm cells you would hit during the shift (ultimately when fueling resumes when letting out the clutch). This is a strategy that has also been used by some to attempt to combat the infamous "shift knock" that can occur even without FFS. Try logging only RPM, load, and clutch switch (nothing else to maximize resolution) and you'll get a general idea of what areas of the timing map you are hitting during a shift.

Bill
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Old 06-15-2011, 08:41 PM   #5
WrXtaCy2003
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I'll do that, thanks!

DK
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Old 06-29-2011, 02:06 AM   #6
WrXtaCy2003
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I've tried all with no avail. I even put in race gas with the new lower timing map and it did not get ANY better. The ONLY way to not have knock is when I turn the FFS to 6k, and thus it does not bounce off the limiter before I shift, but then there is a slight hesitation. I tried shutting off all KC, but it still pulls timing at the FFS. Am I missing a table or something,or maybe editing the tables incorrectly, or can KC not actually be turned completely off? I'm going to the track again tomorrow, and would like to solve this by then, or if not atleast be able to just shut KC off for the track.

Thanks.

DK
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Old 06-29-2011, 09:20 AM   #7
Cobb Tuning
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Originally Posted by WrXtaCy2003 View Post
I've tried all with no avail. I even put in race gas with the new lower timing map and it did not get ANY better. The ONLY way to not have knock is when I turn the FFS to 6k, and thus it does not bounce off the limiter before I shift, but then there is a slight hesitation. I tried shutting off all KC, but it still pulls timing at the FFS. Am I missing a table or something,or maybe editing the tables incorrectly, or can KC not actually be turned completely off? I'm going to the track again tomorrow, and would like to solve this by then, or if not atleast be able to just shut KC off for the track.

Thanks.

DK
Yes, you can completely turn it off, although we don't generally recommend this. First you need to determine which knock response is pulling timing. It will be either feedback knock correction, fine knock learning, or the DAM. If it is feedback correction, then you can modify the "Feedback Knock Retard Activation (RPM Range)" table. If you do not have this table or it is not exactly named as shown, then you have an old version of the software and must update by re-submitting a request for ATR. In this case, to restrict the range that feedback knock correction will occur, you would lower the last two values to the max RPM you want. For example, if the stock values are 6300/6400 and you wanted to deactivate it below 5000, set it to 4900/5000. The 4900 RPM in this example indicates when feedback correction will re-enable when dropping from above 5000 RPM (so you can set this closer to max value if you want).

If it is fine knock learning you want to disable, it is a little more tricky. This is a learned value so the RPM range ("Fine Knock Learning Modify (RPM Range)") simply determines when a change to the learned table can take place. However, the learned value is applied across a specific load/RPM range (per cell), so you have to take into consideration these ranges in the tables, otherwise, a correction could still be applied to the RPM range that you wish to restrict. For example, the RPM range for one of the cells could be 5600-7000 RPM. If you lower the "modify" RPM range to 6000, the ECU can still learn in this cell from 5600-6000 RPM and it will be APPLIED to the entire cell (5600-7000 RPM). You can see the RPM/load ranges by looking at the "Fine Knock Learning" table in ATR (if you live connect, you can see the current values in the table). It may be that you have to modify the axes values in the "Fine Knock Learning" table as well as the "...modify (RPM Range)" table to achieve the desired effect.

If it is the DAM dropping, you can simply lower the RPM (last two cells) in the "Coarse Knock Learning (DAM) Modify (RPM Range)" table. Keep in mind that the DAM will still drop to an initial value post-reset, post-reflash or when you disconnect the battery.

Bill
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Old 06-29-2011, 05:16 PM   #8
WrXtaCy2003
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Hey Bill, thanks for the quick response. It is ONLY FBKC, no FLKC or DAM KC.

In your sentence,

" For example, if the stock values are 6300/6400 and you wanted to deactivate it below 5000, set it to 4900/5000. The 4900 RPM in this example indicates when feedback correction will re-enable when dropping from above 5000 RPM (so you can set this closer to max value if you want)."

Did you mean to say, "deactivate it above 5000"?? I would like to shut it off, say anything above 1000rpm? So, I would have NO FBKC from 1000 and above...this it what I would like.

Thanks.

DK
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Old 06-30-2011, 09:28 AM   #9
Cobb Tuning
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Originally Posted by WrXtaCy2003 View Post
Hey Bill, thanks for the quick response. It is ONLY FBKC, no FLKC or DAM KC.

In your sentence,

" For example, if the stock values are 6300/6400 and you wanted to deactivate it below 5000, set it to 4900/5000. The 4900 RPM in this example indicates when feedback correction will re-enable when dropping from above 5000 RPM (so you can set this closer to max value if you want)."

Did you mean to say, "deactivate it above 5000"?? I would like to shut it off, say anything above 1000rpm? So, I would have NO FBKC from 1000 and above...this it what I would like.

Thanks.

DK
Sorry, yes, that should read "deactivate it above 5000". I wouldn't recommend shutting it off from 1000 RPM on. Keep in mind that feedback knock correction is the default correction. If you shut it off and conditions do not dictate that changes to the DAM or fine knock learning are allowed, then the ECU will do nothing in response to knock. For example, if load is rapidly changing (such as at WOT), the ECU will not use the DAM or fine knock learning to respond to knock. It reverts to the default feedback correction. If you shut it off, you will have no knock response in that scenario.

Although we don't recommend lowering the max. feedback RPM range, if you must do it, I would lower it only as low as needed to avoid the correction when FFS is active. Either way, I would run some partial race gas if you can when you take it to the track as an added measure if you plan to neuter a portion of the knock response.

Bill
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Old 06-30-2011, 03:50 PM   #10
WrXtaCy2003
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Thanks again. I was able to get it shut off last night for the track. I was on 100oct, but the tune was still my 93 tune, so I was 100% confident that my motor would be fine shutting off knock correction. The car never knocked doing pulls in any gear EVER, only on FFS, even after lowering the timing, and seeing in the logs it actually running the lower timing when coming back off the FFS.

Thanks.

DK
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Old 06-30-2011, 04:04 PM   #11
Phatron
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I've never had luck with LC or FFS in Cobb or OS.

Knocks on e85 and c16. Tried lowering timing, adding fuel, changing avcs, basically everything i could think of and none of it had any effect.

I gave up and just advise people not to use it....or to put the race gas in and turn off the KC.
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Old 06-30-2011, 08:52 PM   #12
WrXtaCy2003
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Thanks, that's really nice to know considering cobb's first post said they "could never replicate this in house". I just kept thinking in my head that when I worked at pandL I remember hearing about this issue a lot, but I was on my aem at the time so I didn't care. I'll stick to shutting of KC when at the track or pwning noobs, I'll be on e85 shortly too.

DK
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Old 07-01-2011, 02:11 AM   #13
Cobb Tuning
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Thanks, that's really nice to know considering cobb's first post said they "could never replicate this in house". I just kept thinking in my head that when I worked at pandL I remember hearing about this issue a lot, but I was on my aem at the time so I didn't care. I'll stick to shutting of KC when at the track or pwning noobs, I'll be on e85 shortly too.

DK
Certainly we've heard of the issue you've been experiencing, but, during development, we did not see it on a 2011 STi, 2008 STi, 2002 WRX and 2004 WRX. We also had a closed beta test with customers who were willing to try it out where it did not occur to our knowledge. And to date, since the latest LC/FFS release, I only remember a couple of people potentially experiencing this issue (yours included).

That said, we are always looking for ways to improve these features and welcome any and all feedback. While we are working on other highly demanded features right now (such as speed density), we could certainly revist LC/FFS down the road. A possibility could be adding the capability to disable FBKC/FLKC/DAM changes when LC/FFS is active. Some have reported that the issue responds to timing/fuel changes, so, for those cases, a timing/fuel comp when LC/FFS is active may be useful.

Bill
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Old 07-01-2011, 03:38 PM   #14
WrXtaCy2003
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Thanks, but I would like you guys to put all efforts into speed density , I'm OK with shutting of KC for track usage.

DK
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