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-   -   Stutter, Studder, Hesitation... etc (http://legacygt.com/forums/showthread.php?t=198070)

SeeeeeYa 12-14-2012 06:37 AM

Stutter, Studder, Hesitation... etc
 
It seems to me I've been reading about this subject forever... or however long I've been on these forums. From zero problems to bad enough to get rid of the car, the issue of an RPM-dependent engine-smoothness problem has either plagued or threatened a huge segment of the Subaru Community.

It has taken many years and an unorthodox approach, but a solution has been found recently. The links to the threads specifically dealing with this solution at the moment are:

Start here, with the post by XNWRX near the bottom:
http://www.romraider.com/forum/viewt...4911&start=240

Here:
http://www.iwsti.com/forums/2-5-lite...an-spot-5.html

And here:
http://www.iwsti.com/forums/2-5-lite...rd-line-6.html

As most know, the RR thread has been devoted to a software solution since 2009. While this newest revelation also involves changing and flashing a new map, it is a mechanical solution and the "tuning" is only necessary to remove the OEM ECU "crutch."

The change in my own, excellently running, engine performance was, in a word, astounding.

JermTheElf 12-14-2012 06:47 AM

Very interesting. That "stub" idea is really cool.

cryo 12-14-2012 06:50 AM

Sub'd

Always good to see you posting seeya.

Arnt those tables exclusive to 07+ ecu's? Glad to see it helped in your situation though.

Dave

SeeeeeYa 12-14-2012 07:24 AM

Quote:

Originally Posted by cryo (Post 4203349)
Sub'd

Always good to see you posting seeya.

Arnt those tables exclusive to 07+ ecu's? Glad to see it helped in your situation though.

Dave

Good question. One would think that, like other things, Subaru may never have had a reason to address the fuel resonance problem "back then," and thus either the Load Compensation tables involved don't exist in early ECUs or have not been revealed.

Nevertheless, there is every reason to suspect that even earlier cars without those tables defined still have the same problem, that can be removed with the addition of one meter of FI hose. Nothing to lose, a LOT to win.

Those with the tables can see the resonances revealed by zeroing out the subject tables. Because ATR leaves untouched cells green, cells that have gone more positive red, and cells that have gone negative yellow, a pattern in color is revealed after zeroing the table.

I mentioned I ruined my OEM quick-connect short hose... I did that by trying to use a barbed connector. The trouble is, the new 5/16" hose is larger than the OEM line. In addition, the OEM line is lined... with a very unforgiving liner, that tears easily, potentially releasing pieces into the injector supply that could spell death to an engine if it blocks one. Just remove that section altogether, and install the new hose as I explained. (It goes without saying, but... I also made CERTAIN there was nothing in the new hose before I installed it.)

cryo 12-14-2012 07:43 AM

Yeah i have been following the threads on other forums for a while as well. Im hoping a few people in 05/06 models are willing to give this a shot that suffer from it and report back.

Dave

Berzerklo 12-14-2012 04:44 PM

Harmonics are a fickle beast. I need to get off my OTS tune ASAP! Very interesting stuff. Thanks for posting OP.

cryo 12-14-2012 05:42 PM

1 Attachment(s)
The 05/06 models have it as well although not a cruise/non cruise style. It also maxes as 2000rpms stock. I Was in the middle of building a map so I figured I would check and confirm. Looks like it may be an option as well for those who suffer from it. I've never spent too much time trying to tune around it because no one had found the mechanical issue causing it, I hope this turns out to fix it once and for all.


Dave

SeeeeeYa 12-14-2012 06:55 PM

Quote:

Originally Posted by cryo (Post 4204384)
The 05/06 models have it as well although not a cruise/non cruise style. It also maxes as 2000rpms stock. I Was in the middle of building a map so I figured I would check and confirm. Looks like it may be an option as well for those who suffer from it. I've never spent too much time trying to tune around it because no one had found the mechanical issue causing it, I hope this turns out to fix it once and for all.


Dave

After doing some checking myself, I note that Cobb's latest STi tune has both tables retuned from OEM... shifting compensations to apply at different RPMs. Other tunes for other cars seem to vary similarly, all trying to account for an itch no one seemed able to locate to scratch. Until now.

Considering how high the compensations are, how focused they are cell-to-cell, one would think that zeroing these tables would create chaos in an otherwise stock fuel system... never mind a stutter or two. But in fact the opposite is true when the extra fuel line is installed AND the tables zeroed... the engine becomes incredibly smooth.

One of the things I always check are Cyl 3&4 Knock Sum totals. I don't record them but they tell me things after enough time. Oddly, while these totals include actual accountable knock events, they're most often elusive to pinpoint. What stands out in the little driving I've done since installing the fuel line is how LOW the Knock Sums have become. No other tuning I've done has impacted this parameter as significantly as this mod.

I haven't mentioned how different the idle has become, but it has... and there was nothing wrong with it before.

It makes sense to me... considering what was going on "backstage" as the Load Compensations played a virtual song with the injectors, modifying fuel independently from all other tuning inputs... instead of being the regulated standard most think our fueling depends on. Wrong. Wrong that causes unexplained low level knock... when the Load Comps are not in sync with engine reality. Wrong even in the best of circumstances, like when there is no egregious Studder to complain about... because behind the seemingly smooth engine is in reality a granularity, or continuous background of fueling errors. The difference between unfinished wood and a polished handrail.

In short, it is simply not possible for any car with these tables active to operate smoothly... in the manner of a polished handrail.

cryo 12-14-2012 07:49 PM

I agree and hope this might be a solution to why these tables were populated in the first place.

Dave

O.C.D. 12-14-2012 08:53 PM

::munch::munch::munch:

Aracheon 12-15-2012 12:02 AM

This is interesting. I've been seeing weird spikes in knock events (with E85) just cruising down the highway. I'm running the AEM FPR with -6AN SS feed and return lines that are the same length, if not a little shorter than the stock ones. I've wondered if integrating a damper back into the system would have made a difference in those readings. I've got a fairly decent length of -6 hose left... mayhaps I should try that to see if it changes anything.

rtbrjason 12-20-2012 11:49 AM

1 Attachment(s)
Thanks for alerting me to this thread SeeeeeYa!

I've been logging/tuning the Engine Load Comp table for years trying to get it dialed it. I've got hundreds of megabytes of data and have made hundreds of revisions just to this table. I always felt a bit like I was chasing my tail with this, and my table has what I'd consider absolutely ridiculous values to make it run smooth.

I finally reached out to someone smarter than me on the RR forums a year or so ago to see if there was some chance my car had a cruise/accel table that weren't correctly defined as I only have one Engine load comp table in my 08. Unfortunately nothing was found.

I've not tried the mod yet, but it seems easy and cheap enough, though I'm not entirely sure how to deal with the fuel quick connector. I noticed that when the car came back from a longblock replacement, the lower (return line) fuel quick connector was attached crooked and it always bugged me. I never did anything about it as I didn't have the correct tool. What are people using to remove these other than sliced portions of Bic pens? Is there a specific size the tool needs to be?

SeeeeeYa 12-20-2012 02:14 PM

Here is what I did with the line: http://www.iwsti.com/forums/3736324-post48.html

Depending on the results of your mod (going to assume here) you can make an important contribution to the LGT database.

I am going to bet you see significant improvement. :)

mmmmspecb 12-20-2012 02:26 PM

Hmmm,

Tagging this for later viewing. I'm starting to get this problem creep up again.

Aracheon 12-20-2012 06:25 PM

I'll be replacing the fuel line tomorrow, so count me in for reporting findings as well.

(My under-hood fuel lines were replaced with -6AN braided stainless ones, so swapping around is super easy.) Just have to figure out how to properly coil and secure that much hose.

Now, one interesting thing, is that in ATR, I'm only finding ONE load compensation table, not two like there appears to be in the GR STi ECU. Is this correct?


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