The Stumble/Stutter Thread

[O.C.D.]

I did the fuel line mod, and it made zero difference in the running characteristics. Next step is to flash my ECU.

 

I'm frustrated and running out of ideas.

 

I am in your boat as well. About to lose it.

[rtbrjason]

I am in your boat as well. About to lose it.

 

Are you using Tactrix or Accessport?

[BlackWagon GT]

Since the data that has come out of my ECU has yielded no clues, I'm starting to wonder if I am looking in the wrong place to find the problem. I did some thinking tonight, but what if it's actually a mechanical issue rather than tuning/software? The dual-mass flywheel specifically came to mind. It's a shot in the dark, yes, but taking its construction into consideration, I would posit that a worn or damaged DMFW coupled with some driveline slack might just be enough to cause oscillation.

 

I could be way off, but when the obvious answer is wrong, it's time to start thinking outside the box.

[Skidude]

I had that thought as well. Does anybody with a standard flywheel have the problem as bad?

[Brprs]

What about the auto dudes?

[Aracheon]

What about the auto dudes?

 

 

 

Isn't this issue more prevalent with the 5MT guys?

 

Sent from my SCH-I535 using Tapatalk 2

[SeeeeeYa]

Isn't this issue more prevalent with the 5MT guys?

 

Sent from my SCH-I535 using Tapatalk 2

 

You are aware of the other active threads about this, right?

 

Obviously, manual transmissioned cars have a greater sense of engine performance because they have a direct connection from the engine to the wheels. And just as obviously, the automatic transmissioned cars have a slushy connection.

 

But. Their fuel systems are identical. Consider.

[BlackWagon GT]

Obviously, manual transmissioned cars have a greater sense of engine performance because they have a direct connection from the engine to the wheels. And just as obviously, the automatic transmissioned cars have a slushy connection.

 

You raise one point and give credence to mine at the same time.

 

If you are correct, then the problem, or I should say a variation of the symptom, is nonspecific to either type of transmission but is simply buffered by the torque converter so it appears that manual transmission cars are more symptomatic.

 

However, if there is a symptom variation that is specific to MT cars, then that would give more weight to the possibility that it could be caused by a faulty DMFW since it is the only factory-installed directly-coupled component that is not present with an AT.

 

Cruising these threads has led me to believe there are multiple causes and therefore multiple solutions to similar symptoms. The problem is, without directly experiencing the symptoms side-by-side, we are all attempting to interpret other people's descriptions to make armchair diagnoses. I know I certainly fall into that category.

[SeeeeeYa]

You raise one point and give credence to mine at the same time.

 

If you are correct, then the problem, or I should say a variation of the symptom, is nonspecific to either type of transmission but is simply buffered by the torque converter so it appears that manual transmission cars are more symptomatic.

 

However, if there is a symptom variation that is specific to MT cars, then that would give more weight to the possibility that it could be caused by a faulty DMFW since it is the only factory-installed directly-coupled component that is not present with an AT.

 

Cruising these threads has led me to believe there are multiple causes and therefore multiple solutions to similar symptoms. The problem is, without directly experiencing the symptoms side-by-side, we are all attempting to interpret other people's descriptions to make armchair diagnoses. I know I certainly fall into that category.

 

To be honest, to some degree I am humoring your position. If you have read the various threads, and the results of those responding, it should become clear that there is a fact established; the fuel line mod works. Period.

 

This is not my mod. I am merely vocal about my personal success and offer my own results so others can decide for themselves their own course of action.

 

If it is not clear to you then by all means continue to pursue your own research. Meanwhile the overwhelmingly positive results predominate.

[m sprank]

If your tests have only been performed on your STi than the results are not valid for sidefeed injected LGT's. The fuel rails and piping and FPR and lines are different. If someone has tested (and performed a test with repeatable results) on a side feed injected LGT that is different.

 

Just saying.

[SeeeeeYa]

If your tests have only been performed on your STi than the results are not valid for sidefeed injected LGT's. The fuel rails and piping and FPR and lines are different. If someone has tested (and performed a test with repeatable results) on a side feed injected LGT that is different.

 

Just saying.

 

From rtbrjason's post here: http://legacygt.com/forums/showpost.php?p=4220022&postcount=119

 

One thing I have noticed is considerably less knock sum increments in the 2700-3200 rpm range where I had constant issues with knock at 1.1-1.3 load while mildly accelerating on the highway. I never believed this was real knock but it seems to be completely gone whereas prior to this mod I could make knock sum increment every time I hit 2700 rpm and 1.3 load.

 

It was his input that modified the "zeroed-out" advice earlier posts advocated, in my own tune. His input is thorough, the result of good work and intelligent tuning. Most of the posts here, in the LegaciyGT forums, chronicle frustration, and the belief they're "different" somehow.

 

rtbrjason hints this isn't totally true.

 

rlefevre states:http://legacygt.com/forums/showpost.php?p=4216619&postcount=109

 

Another hint.

 

It seems to have worked well for me

IMO it will work even better with his LC tables modified appropriately.

 

Time will tell.

[m sprank]

rtbrjason has an 08. So top feed injectors with the change to the rails, piping, fpr, lines etc from the factory. I own 2 08's. A SpecB and a 5EAT. Never had any stutter/stumble issue. Not even when they were stock. My 05 5EAT never had the issue either.

[SubaruFirst]

Under TurboPowerTrains by sticky there is a sttuter thread. It's about the fuel pump speeds and problems with voltage drops . I see that thread to be part of this problem possibly.

[KCwagon]

Under TurboPowerTrains by sticky there is a sttuter thread. It's about the fuel pump speeds and problems with voltage drops . I see that thread to be part of this problem possibly.

 

The above mentioned thread is not a stutter thread. It was created to address the issue of the proper amount of voltage going to the pump. A solution was also discussed which involves using a FPCM from an STI and powering it directly from the battery. There are a few of us who have actually torn apart our cars and done this successfully.

[rlefevre]

I installed a cobb dp today and stage 2 map to see if it would further improve my stutter situation. I had it almost completely eliminated with the stock setup, but I had already purchased the downpipe so I went ahead and installed it. I have not driven a whole lot yet but so far I have had no stutters.

 

I have also been modifying the load compensation tables based on that excel spreadsheet floating around here somewhere where you datalog and then it makes recommendations to change the values in the table. This seems to have worked better for me than zeroing the table.

 

I know the fuel line mod has not worked for everyone, but for me, doing that and modifying the LC tables has made it a whole new car.

[BX77]

DP work out well?

[rlefevre]

Yes it fit right up with no issues.

[BlackWagon GT]

rlefevre, you have an '09, correct?

 

I have attached a few logs I made today. I found out that my AP will only log up to 16 points, so things I wanted to include like cylinder roughness didn't make the cut. I can always change the point list and re-log if it will help to figure out what has been so elusive so far.

datalog46.csv

datalog48.csv

datalog50.csv

[rlefevre]

Yes 2009 5EAT.

[SeeeeeYa]

rtbrjason has an 08. So top feed injectors with the change to the rails, piping, fpr, lines etc from the factory. I own 2 08's. A SpecB and a 5EAT. Never had any stutter/stumble issue. Not even when they were stock. My 05 5EAT never had the issue either.

 

You know, I said much the same for years. I have read about the studder issue from when I had my 05 LGT, the 11 WRX, and especially including this 11 STi... and was quietly glad I didn't know what anyone was talking about. From my perspective I didn't have any such issue.

 

Then last December I happened across the fuel line chatter. The explanation in the big RomRaider thread made it clear there was, in fact, a physical event going on inside the fuel system. No matter how great my car worked changed the fact I had the same fuel system. I must, therefore, be being affected even if I couldn't see it. I had no idea what would happen differently, but I had to find out.

 

My results are posted in a number of threads now. To me they are significant, almost too good to be true. But I admit that what I find so great, a lot of people would neither see, nor experience the results I find so transforming. It is a case of, seek and you will find... with the devil in the details.

Edited January 14, 2013 by SeeeeeYa

[m sprank]

I normally see approx 5-7 Subies a day at the shop. I have had ZERO customers complain of this "stutter" issue at the shop. While Shamar has tuned plenty that complained of it, afaik most (if not all) said it was gone with the tune. If I can find one stuttering and get to "play" with it myself, I will deff test the mentioned "fixes".

[BlackWagon GT]

I actually have a follow-up question to my previous post. What does "A/F Sensor Current" represent? Is it the sensor heater or the raw output from the sensor element?

[SeeeeeYa]

I normally see approx 5-7 Subies a day at the shop. I have had ZERO customers complain of this "stutter" issue at the shop. While Shamar has tuned plenty that complained of it, afaik most (if not all) said it was gone with the tune. If I can find one stuttering and get to "play" with it myself, I will deff test the mentioned "fixes".

 

While the condition obviously exists in LGTs, it is also obvious it is nowhere near as much a problem as it is for STis. Plus, what problems LGTs do have, as you say, is confused by other issues... and everything gets put into one basket.

 

Infamous may also have solutions of his own, included in his tune, that comes from his experience with these cars, and an Infamous tune a relatively inexpensive route to a solution.

 

But if you do get to play with one with an obvious studdering issue, your input would be invaluable and further refine the information for the LGT platforms.

 

Meanwhile, there is no harm nor any potential introduction of negatives if people with conditions they term studdering install the fuel line and modify their LC table. So far, although studder, specifically, has not shown an impact like the STi crowd, certain other benefits have been noted.

[m sprank]

Nothing against modifying fuel lines. Use the proper line and all is good. Like i said, we tend to reroute lots of fuel lines. I have a pet peeve about them being stretched or rubbing on FMIC piping.

 

I will ask the 08+ WRX/STi owners that come in too. We dont just work on LGT's. They are Shamars "bread and butter", but I see all the models all day. Currently I have 1 '05 STi (42r rotated), 1 '07 STi (full race twin scroll rotated), 1 '05 WRX (stage1), 1 '02 WRX (stock) and 1 '06 WRX (built motor with 6MT swap, FP Green) at the shop. 1 2010 LGT came in today (stock).

[GEE-OTTO]

Hello folks ,

 

Not sure if you can help but i didnt want to start a new thread and this is very similar to my problem except, dare I say, I'm N/A:eek: So....

 

Car: 09 2.5i 5MT

Mile: 124K

Symptoms: When in traffic and I stop, RPMs drop then immediately surge to 1500-1700 then dips to 1000 then rises then returns to idle. This only occurs when the clutch is in and in gear (happens in any gear) if I take the car out of gear with foot on the clutch idle drops to normal as soon as I put it in gear (foot on clutch) the jump back up then exhibit above described beahvior.

 

My question: COuld logging give me some insight as to what makes the ECU surge the throttle?

 

 

Checked the Throttle body and it is clean, no vacuum leaks and MAF has been cleaned. Since the action of pushing in the clutch and the car being in gear seems to cause this behavior could there be something wrong with the clutch pedal switch ?