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-   -   *** Knock, do you have any? (http://legacygt.com/forums/showthread.php?t=97539)

LittleBlueGT 10-05-2008 06:00 PM

*** Knock, do you have any?
 
I have learned the hard way, and so have a few others. Now that another local has blown a stock block I think this problem should be addressed.

How do you know if your engine is experiencing detonation (knocking)?

-you log it!


Seems simple, but many people miss a few important bits of info. Yes all this info is in threads like Subaru's Knock Control Strategy Explained at RomRaider. But let's make it a bit simpler so even the basic guy that wants a strong running stage1 or stage2 can figure it out.

First myth (that seems to get carried around, and expounded upon from time to time, even by people that should (and maybe do) know better:

"My car is showing positive DA (Dynamic Advance), I guess all is well"

WRONG! That statement could be true, but just as easily could be false.

Let's look at an example:

Here is a little log showing DA, I have heard others say, "look at how happy the ECU is, it is adding 8 degrees of timing almost all of the time!"

http://i248.photobucket.com/albums/g...luegt/DA-2.jpg

Here is the exact same log, but this time FBKC (Feed Back Knock Correction) is added to the list of logged items:

http://i248.photobucket.com/albums/g...t/DA-2FBKC.jpg

Same log, same everything, but now it is readily apparent that at 5219 rpm the ECU heard what it thought was a knock event, and pulled 2 degrees of timing as a result.

That same info could be seen in the first log, but it is a bit harder to see. First of all I know that my high load DA table is all 8s, so at high load if my DA is anything but 8 degrees, I know there is a problem. Second, one can graph out the timing, and from there it is easy to see that the ECU pulled 2 degrees of timing.

"But it was easy to see the pulled timing, even w/o logging FBKC.
"

In this log that may be true, but it is not always that easy to see. For one thing, not all tunes are set up the same (not saying one way is better then another). This can get more complicated, but lets just leave it at that.

I think for the "Joe Blow" that just wants to quickly see if things are safe it is much easier to log FBKC and be done with it. Of course one should also make sure their IAM is at 1.0, and it is a good idea to look at one's learning view. All are addressed in other threads.



Cliff notes:

1) log or learn how to log, or have a buddy log your car, even if you are just running COBB stage2 (our gas doesn't even like COBB's tune)

2) if you only have COBB logging ability, then learn how to read the logs properly to determine if there is any knock.

3) RomRaider is the best tool IMO to use for logging, use it to log FBKC

4) if FBKC is 0 for a WOT run, IAM is at 1.0, and your learning view loks clean, then it is pretty safe to say your engine saw no knock for that logged run


Hope this saves a few blocks.:)

SeeeeeYa 10-05-2008 06:21 PM

Good thread as usual LBGT.

But if there is such a thing as DA, FBKC, and all the rest of Subaru's knock handling ability, for which it is much praised, then why the concern? There are even special maps for when knock gets so bad all the normal maps don't work anymore. Given the variability in fuels these days, added to all the environmental variables, it would seem impossible for any car to be det free all the time.

Back when I got my AP the Cobb maps almost always had some pulled timing. Later, on TDC eTunes the same pattern was there. No one ever said a couple of degrees of DA being pulled was terrible. The only warning was to make sure it never went into MINUS DA.

Is the point of this thread to assist in the development of a well rounded tune? Or is it pointing out that having anything other than perfect DA is a motor killer.

If this motor is that sensitive and that fragile then a) Subaru's knock control is a joke, and b) abandon all hope for a long lasting turbo motor because perfect DA all the time ain't gonna happen.

LittleBlueGT 10-05-2008 06:33 PM

Quote:

Originally Posted by SeeeeeYa (Post 2092025)
Good thread as usual LBGT.

But if there is such a thing as DA, FBKC, and all the rest of Subaru's knock handling ability, for which it is much praised, then why the concern? There are even special maps for when knock gets so bad all the normal maps don't work anymore. Given the variability in fuels these days, added to all the environmental variables, it would seem impossible for any car to be det free all the time.

Back when I got my AP the Cobb maps almost always had some pulled timing. Later, on TDC eTunes the same pattern was there. No one ever said a couple of degrees of DA being pulled was terrible. The only warning was to make sure it never went into MINUS DA.

Is the point of this thread to assist in the development of a well rounded tune? Or is it pointing out that having anything other than perfect DA is a motor killer.

If this motor is that sensitive and that fragile then a) Subaru's knock control is a joke, and b) abandon all hope for a long lasting turbo motor because perfect DA all the time ain't gonna happen.

I blew my motor running 2 - 4 degrees of positive DA.

IMO if you have less then perfect DA for anything more then about 10% of your WOT runs something should be changed.

We can (and likely will) get more complicated, but I want to keep this thread simple for the noobs so they know what to look for.

The DA is all about how the tuner set it up. You could have 12 degrees called for, and then only running 6, that would be bad. Remember, that Subaru designed their knock control strategy around an engine making a lot less whp, the more you make, the less room their is for knock.

SubiGT 10-05-2008 06:52 PM

Thanks LBGT. I just started using RomRaider, and also using much better gas. I'm going to compare my old tune to one I recently got, and see which one the car is happier with. Then we'll adjust from there.

Since I'm new to RR, which parmeters are best to select for the most informative logs? I can see what you have posted above, but those might just be representative of what you are describing for this thread.

SeeeeeYa 10-05-2008 06:53 PM

Oh, I wasn't arguing with you, I totally agree. My intent was to provide you the opportunity to say what you just did :).

There is far too little emphasis put on what you are highlighting here. People are tuning up a storm everywhere with ST, Enginuity, Romraider, cable this and cable that, and are largely unaware of how disastrous their actions can be. Familiarity is breeding contempt for the repercussions.

You may save a bunch of engines if people read and take this seriously.

j255c 10-05-2008 06:55 PM

one thing to account for is not all tuners flatten their knock correction/da tables either to one number.

SubiGT 10-05-2008 07:02 PM

Quote:

Originally Posted by SeeeeeYa (Post 2092070)
Oh, I wasn't arguing with you, I totally agree. My intent was to provide you the opportunity to say what you just did :).

There is far too little emphasis put on what you are highlighting here. People are tuning up a storm everywhere with ST, Enginuity, Romraider, cable this and cable that, and are largely unaware of how disastrous their actions can be. Familiarity is breeding contempt for the repercussions.

You may save a bunch of engines if people read and take this seriously.

I, for one, will always have a professional tune on my car. I might play around with AccesTunerRace(after I get my wideband;)), but the initial tuning of any hardware changes will be done by a reputable pro, on a dyno. Too much $$$ at stake to attempt otherwise.

LittleBlueGT 10-05-2008 07:03 PM

Quote:

Originally Posted by SubiGT (Post 2092068)
Thanks LBGT. I just started using RomRaider, and also using much better gas. I'm going to compare my old tune to one I recently got, and see which one the car is happier with. Then we'll adjust from there.

Since I'm new to RR, which parmeters are best to select for the most informative logs? I can see what you have posted above, but those might just be representative of what you are describing for this thread.

Use FBKC to determine if their is knock. But first check your IAM, and it is a good idea to look at your learning view. You can log Fine Learning Correction (FLC), but IMO it is better to just look at it before you log.

You can also use knock sum to determine if the ECU thinks there is knock, is some cases (not really WOT stuff) it can be very useful as there are no filters applied like there are for learned knock and FBKC.

SubiGT 10-05-2008 07:05 PM

Thanks.

+1 Sticky

Infamous1 10-05-2008 07:15 PM

Stuck...

j255c 10-05-2008 07:17 PM

excellent work. :redface:

NSFW 10-05-2008 10:42 PM

You mention the "learning view" utility but I think it deserves a little more detail. And I could use a sanity check on my own understanding of it - so if this is wrong please let me know:

The Learning View utility will display your Fine Learning Knock Correction (FLKC) table, which shows the RPM/Load areas in which the ECU has learned to pull timing in response to knock. It will also show your Ignition Advance Multiplier (IAM), which should be 1.0 but will drop if your car has experienced significant knock.

Learning View connects to your ECU using an OpenPort 1.X or compatible cable, much like RomRaider's logger. The VAG-COM cable will probably also work, and OpenPort 2.0 compatibility is likely coming soon.

For more information, and a link to download the Learning View utility:
http://www.romraider.com/forum/topic2772.html

If you are tuning your car, you should use this periodically to see if your engine has experienced knock when you were not actively logging. If you see evidence of significant knock, it's time to reconsider your tune.

The stock tune will show small amounts of knock correction (-.35, -1.05, etc) occasionally in various cells, these are not cause for great concern. But IAM under 1.0, or larger corrections in the FLKC table, should be investigated. The Learning View thread (linked above) has a lot more information and examples to show how to interpret Learning View results.

Learning View also shows your fuel trims, which are primarily of interest if you have changed your intake tract or fuel injectors. If they're way off (more than 5%) you may want to address that, but this is another subject for another thread.

Note that resetting your ECU (which happens during reflashing, for most ECUs) will set IAM to 0.5 (or whatever your ROM has configured for the initial IAM) and will clear the FLKC table. Don't panic if you see a low IAM soon after a reflash. :)

SlightlyEvil 10-05-2008 11:01 PM

This thread is great. As "Joe Bloe" (european spelling) tuning and the variables involved always seem shrouded in the same sort of confusion that prevents me from reading sheet music - I dunno what all the abbreviations and symbols mean and I don't care enough to sift through it. So a straight forward explanation like this is really helpful. Thanks!

Logged my protune and IAT at 1 I see 0 through the entirety of the WOT runs for FBKC so that's one more step on the road to feeling confident in my car. :)

j255c 10-05-2008 11:10 PM

Thats what these guys are here for. This is a great thread for the community.

merchgod 10-06-2008 06:45 AM

One thing that is commonly missed is that changes to FBKC, changes to FLKC, and changes to the IAM are all three separate knock responses and only one is active at any given time. So, if you look at only FBKC, you are not getting the whole picture. FBKC is not the response to ALL knock events, it is the response to knock events when it happens to be active. This is all based on a number of conditions that are outlined in the knock control sticky. That is, the ECU, at any given time, is "poised" to respond to knock events using only one of the three knock control elements OR it is "poised" to do nothing at all in response to a knock event (say at low RPM).

Another common misconception is that the ECU will make a change to FLKC or the IAM based on FBKC. This is false. The ECU could care less what FBKC is at any given moment - it could be -2, -12, doesn't matter, it is not going to change FLKC or IAM at all. That is because FBKC, based on those conditions in which it is active, is the proper response given those conditions. Only changes to the FLKC and the IAM are linked. IAM can be thought of as a means of get timing roughly where you need to be and then FLKC does the finer adjustments. This is why the entire FLKC table is cleared when the IAM changes.

It is more difficult to determine when the FLKC changes because when you log it, you are logging the applied (learned) correction for the currently accessed cell. You can log 'fine learning table offset' and if the offset stays the same and FLKC changes, then a change was made to that cell. Easier, as already mentioned, would be to check a learning view before and after the run.

With the latest RomRaider logger definitions, I added the 'knock sum' parameter. All USDM Legacy GTs support this parameter. It is easily your best bet to track knock events because it deals with the knock signal which is exactly what determines a knock "event". Changes to FBKC, FLKC and the IAM are all based on this same knock signal. If your ECU support the knock sum, this is the only thing that I would log (while doing a learning view snapshot before and after the run). It will also improve your sampling rate because it is a 1-byte parameter. The only downside is that it will not increment with consecutive knock events, but this is not generally an issue.


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