The Stumble/Stutter Thread

06 Legacy GT manual trans. Have tried many different things just looking for more ideas.

 

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: Will occur under 30-50% throttle between 2000-3000RPM. Mostly noticeable 2500-3000. Can even see the tach jump up and down.

 

MODS

Intake:Stock

Exhaust: Catless up and down pipe

Fuel:Stock

Turbo:VF52 with Grimmspeed EBCS

Engine Management:Cobb AP

Tuner and revision of tune(if you don't mind: E-tune. Still in the tune process but he doesnt think any more changes can be made to help resolve it.

 

MAINTENANCE

Sensors changed:MAF, front O2,

Plugs changed:new NGK 7913 gapped at .030

Coil Packs changed:All new

 

OTHER SYMPTOMS

Check Engine Light:One morning it set a P2007 TGV valve stuck closed and car was in limp mode with maybe 6psi of boost during this time the stutter would not happen not sure if that could point to anything or just cause it was low on power would not happen. Ended up being a bad TGV senor. Once replaced stutter was still there.

Etc:

 

RESULTS

What has and hasn't worked for you: I have moved the FPR vacuum line to be teed into the BPV hose. Bought the 07 STI FPR and revamped the hoses. Has new OEM injectors. Verified camshaft timing. I own a 05 LGT auto so I have swapped several parts from that to this car like BPV, MAF, O2.

 

If something worked, how long has it been working for:Nothing has really changed it. Only thing to note is when using the AP is you pull 5 degrees of timing out it is worse.

I went and looked at my AVCS map and it’s already at 25* in the area I get stumble (.8-1.2g/rev 2000-3000 RPM). Maybe that is too much advance?

 

Try reducing AVCS to 10* for those ranges. Depending on your timing map, you might need to adjust it too. If your timing was fine tuned for the high AVCS then increase timing by about 2* for every 5* of AVCS that you reduce.

 

Interestingly enough, after I installed a stage 2 downpipe on the stock turbo, my car became less tolerant of high AVCS. With a much bigger turbo it's still just as intolerant of lots of AVCS still.

 

I doubt that it's too much, because my wife's 09 LGT has 40 degrees from .5 to .8 in that RPM range. But it couldn't hurt to experiment with 20 and 30 to see if it gets better or worse.

 

It might be interesting to try varying the timing too. For comparison, my wife's car's factory tune (stumble free) has about 30 degrees at .8 r/rev and 16 degrees at 1.2 in that RPM range. My car (pretty good but still experimenting) has about 35 and 15. All of those figures include the base + advance timing values.

 

05-06's hate a lot of AVCS, especially with stock headers. I think the reason 07-09's can tolerate 30-40* of AVCS is due to variable TGV's (and they are usually closed at the the 30-40* AVCS ranges).

 

You can see the same trend in the cruise timing map for 07+, notice a big timing spike up when AVCS goes below 30*.

That's interesting about the TGVs, I hadn't thought of that but you might be right. And I would expect better atomization to help mitigate stumble.

 

Almost makes me wish I hadn't deleted mine, just so I could play with them.

I still have my original ones on the shelf, but I didn't think the 05 ECU could be made to have variable TGV's.

 

Looking closer at 07+ maps, while the cruise map's low timing does coincide with high AVCS, non cruise map also has 30-40* AVCS, but the timing didn't drop like a wall. Now I'm thinking the cruise map's timing wall at 3600rpm might indeed be related to TGV's being closed and tumble action increasing burn efficiency. Unless the non-cruise map is never used during cruise conditions and was just not fine tuned in those areas.

 

Either way, if TGV's do increase burn efficiency by that much to need 10-22* less timing, that area is gonna be far more sensitive to more efficiency increasing mods (ie intake, turbo, exhaust). Installing any of those mods would make the area be over-advanced and knock prone (which can lead to the infamous stumbling).

I had somewhat noticeable stumbling with a previous tune (bnr16g, dw650s, walbro). To the point that I avoided certain brands of gas because it made it worse. After a re-tune (with multiple revisions, 5EAT requested-torque adjustment, etc), it's much, MUCH better. I have also moved FPR to the intake, have my boost gauge off cyl #4, and did the "$0.16 BPV mod". Probably still there a little, but not really noticeable.

 

 

 

Now if only I could get closer to 30 mpg! Pretty sure my tune is running quite rich, but I'm close to getting rid of the car, so I don't really care that much anymore, and I figure it can't hurt anything too badly - nothing like running lean.

 

 

 

I also had some real bad stumbling due to a faulty injector pack, but that's a different issue.

*accidental double post, noob here* Edited April 4, 2019 by Pleides

*removed because stutter is still there* Edited November 11, 2019 by Pleides

Sometimes after a night cap, I stumble to the bathroom in the middle of the night. Does that count?

Sometimes after a night cap, I stumble to the bathroom in the middle of the night. Does that count?

 

Yes, I would love that right now, but still working away

So... I'm not sure how to explain the stumble...

 

Let's say I'm merging onto the highway in 3rd, I floor it because I want moar powah baby. Then instead of feeling the engine power/boost, I get this stumble. It will stumble between 3k and 4k rpm and then stops stumbling as it accelerates.

 

Sometimes I wonder if it's a boost issue. However, I also wonder if it's fuel pump issue (sometimes when I put my key to ON and you expect the fuel to pressurize, I hear what can only be described as a small whale/dolphin making a low volume mating call off in the distance -- car starts and runs seemingly fine). edit: I should add that if it's cold and if I accelerate up a hill at very low RPM it will surge like no tomorrow.

 

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: both

 

MODS

Intake: stock

Exhaust: stock

Fuel: 91 pump - no noticeable change on 94 pump

Turbo: stock - td04hla

Engine Management: stock -- own a tactrix v2

Tuner and revision of tune(if you don't mind): none

 

MAINTENANCE

Sensors changed: none

Plugs changed: 1 step colder iridium

Coil Packs changed: none

 

OTHER SYMPTOMS

Check Engine Light: nope

Etc: -

 

RESULTS

What has and hasn't worked for you: changed to colder plugs and may have reduced stumble slightly... however, still there

If something worked, how long has it been working for: -

Edited December 2, 2019 by gc8fxt

It might be interesting to get a data log showing that stumble, with these parameters:

 

RPM

MAF

Load(calculated)

Final fueling base

AFR (preferably wideband but the stock sensor is fine for cruise and better than nothing for WOT)

Total ignition timing

Fine learning knock correction

Feedback knock correction

Knock Sum

 

I have a little theory that low ignition timing, caused by knock correction, is a big factor in stumble. It has been for me.

So... I'm not sure how to explain the stumble...

 

Let's say I'm merging onto the highway in 3rd, I floor it because I want moar powah baby. Then instead of feeling the engine power/boost, I get this stumble. It will stumble between 3k and 4k rpm and then stops stumbling as it accelerates.

 

Sometimes I wonder if it's a boost issue. However, I also wonder if it's fuel pump issue (sometimes when I put my key to ON and you expect the fuel to pressurize, I hear what can only be described as a small whale/dolphin making a low volume mating call off in the distance -- car starts and runs seemingly fine). edit: I should add that if it's cold and if I accelerate up a hill at very low RPM it will surge like no tomorrow.

 

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: both

 

MODS

Intake: stock

Exhaust: stock

Fuel: 91 pump - no noticeable change on 94 pump

Turbo: stock - td04hla

Engine Management: stock -- own a tactrix v2

Tuner and revision of tune(if you don't mind): none

 

MAINTENANCE

Sensors changed: none

Plugs changed: 1 step colder iridium

Coil Packs changed: none

 

OTHER SYMPTOMS

Check Engine Light: nope

Etc: -

 

RESULTS

What has and hasn't worked for you: changed to colder plugs and may have reduced stumble slightly... however, still there

If something worked, how long has it been working for: -

 

 

 

I’m having a similar issue I have a 03 BL5 b4 spec B jdm, I did plugs but what I’m thinking is maybe my coils are bad and maybe spark blow out? Seems to only be under boost. I did plugs and maybe that’s my next step [emoji2371]

 

 

Sent from my iPhone using Tapatalk

So... I'm not sure how to explain the stumble...

 

Let's say I'm merging onto the highway in 3rd, I floor it because I want moar powah baby. Then instead of feeling the engine power/boost, I get this stumble. It will stumble between 3k and 4k rpm and then stops stumbling as it accelerates.

 

Sometimes I wonder if it's a boost issue. However, I also wonder if it's fuel pump issue (sometimes when I put my key to ON and you expect the fuel to pressurize, I hear what can only be described as a small whale/dolphin making a low volume mating call off in the distance -- car starts and runs seemingly fine). edit: I should add that if it's cold and if I accelerate up a hill at very low RPM it will surge like no tomorrow.

 

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: both

 

MODS

Intake: stock

Exhaust: stock

Fuel: 91 pump - no noticeable change on 94 pump

Turbo: stock - td04hla

Engine Management: stock -- own a tactrix v2

Tuner and revision of tune(if you don't mind): none

 

MAINTENANCE

Sensors changed: none

Plugs changed: 1 step colder iridium

Coil Packs changed: none

 

OTHER SYMPTOMS

Check Engine Light: nope

Etc: -

 

RESULTS

What has and hasn't worked for you: changed to colder plugs and may have reduced stumble slightly... however, still there

If something worked, how long has it been working for: -

 

 

 

 

Have you logged your actual boost level and boost target? Maybe you are noticeably overboosting in that rpm range, and as a result, the 'turbo dynamic' related variables kick in and try to converge your actual boost level to target, giving you a sawtooth like pattern, resulting in what you described?

It might be interesting to get a data log showing that stumble, with these parameters:

 

RPM

MAF

Load(calculated)

Final fueling base

AFR (preferably wideband but the stock sensor is fine for cruise and better than nothing for WOT)

Total ignition timing

Fine learning knock correction

Feedback knock correction

Knock Sum

 

I have a little theory that low ignition timing, caused by knock correction, is a big factor in stumble. It has been for me.

 

 

 

Have you logged your actual boost level and boost target? Maybe you are noticeably overboosting in that rpm range, and as a result, the 'turbo dynamic' related variables kick in and try to converge your actual boost level to target, giving you a sawtooth like pattern, resulting in what you described?

 

Give me a few days to get these logs. Busy guy.

 

Much of the stumble seems to go away when the engine is fully warmed up but even then it doesn't seem to have the power like I feel it should.

 

My old gc8 with a 20k was rated the same HP as this BP5 with 20Y and although the BP5 is a heavier car, it's not that heavy. The gc8 was silly, though, let's be honest.

 

edit: I did have a 14 FXT and my BP5 does feel quite a bit faster than that so maybe I'm overreacting.

Car is a 2005 Legacy GT 5MT, 142000km. Non-Limited. Recently upgraded to Stage 2.

 

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both:

Steady throttle has no stumble

Increasing throttle has very noticeable flutter/stumble at close to WOT and higher RPMs (4000+)

 

MODS

Intake: Stock

Exhaust: Cobb Catless UP, Cobb High-flow Catted DP

Fuel: Canadian Chevron 94 (currently mixed in with quarter tank of 91)

Turbo: Stock

Engine Management: Cobb AP

Tuner and revision of tune(if you don't mind): Cobb OTS AP Stage 2, 91 ACN map

 

MAINTENANCE

Sensors changed: Original O2 Sensor

Plugs changed: About 30000-40000km ago

Coil Packs changed: Cyl 3 coilpack just changed

 

Recently got fuel system cleaning/oil change from Midas prior to stage 2 (bad idea?)

 

OTHER SYMPTOMS

Check Engine Light: None

Etc:

- Cyl 3 Coilpack was bad, causing misfire code and major stutter at slight throttle at all RPMs. This was just recently changed, and the problem was fixed (this was before going Stage 2).

 

- Pulling with near WOT uphill shows slight knock (-2) with the ACN tune, and up to -6 with normal 91 tune, and you can smell some burning.

 

RESULTS

What has and hasn't worked for you: Nothing has worked so far.. car has about 300km on the current tune and Stg 2 upgrades. Car pulls great and feels smooth for daily driving. Problem only exists when I drive at near 100% throttle doing 3rd gear pulls.

If something worked, how long has it been working for:N/A

 

Wondering if you guys have any ideas. I've attached some logs and based on my research they seem fine, but I'm no expert at reading logs. My mechanic told me to log AFR so will do that tonight, but AF Learning doesnt show anything weird.

datalog45.csv

datalog44.csv

datalog43.csv

datalog38.csv

Edited December 17, 2019 by cvince

Car is a 2005 Legacy GT 5MT, 142000km. Non-Limited. Recently upgraded to Stage 2.

 

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both:

Steady throttle has no stumble

Increasing throttle has very noticeable flutter/stumble at close to WOT and higher RPMs (4000+)

 

MODS

Intake: Stock

Exhaust: Cobb Catless UP, Cobb High-flow Catted DP

Fuel: Canadian Chevron 94 (currently mixed in with quarter tank of 91)

Turbo: Stock

Engine Management: Cobb AP

Tuner and revision of tune(if you don't mind): Cobb OTS AP Stage 2, 91 ACN map

 

MAINTENANCE

Sensors changed: Original O2 Sensor

Plugs changed: About 30000-40000km ago

Coil Packs changed: Cyl 3 coilpack just changed

 

Recently got fuel system cleaning/oil change from Midas prior to stage 2 (bad idea?)

 

OTHER SYMPTOMS

Check Engine Light: None

Etc:

- Cyl 3 Coilpack was bad, causing misfire code and major stutter at slight throttle at all RPMs. This was just recently changed, and the problem was fixed (this was before going Stage 2).

 

- Pulling with near WOT uphill shows slight knock (-2) with the ACN tune, and up to -6 with normal 91 tune, and you can smell some burning.

 

RESULTS

What has and hasn't worked for you: Nothing has worked so far.. car has about 300km on the current tune and Stg 2 upgrades. Car pulls great and feels smooth for daily driving. Problem only exists when I drive at near 100% throttle doing 3rd gear pulls.

If something worked, how long has it been working for:N/A

 

Wondering if you guys have any ideas. I've attached some logs and based on my research they seem fine, but I'm no expert at reading logs. My mechanic told me to log AFR so will do that tonight, but AF Learning doesnt show anything weird.

 

 

It might be related to this:

Have you logged your actual boost level and boost target? Maybe you are noticeably overboosting in that rpm range, and as a result, the 'turbo dynamic' related variables kick in and try to converge your actual boost level to target, giving you a sawtooth like pattern, resulting in what you described?

 

 

Although, looking at your logs, you are not overboosting by much I think. But still, the turbo dynamic stuff will kick in if actual is not equal to target. If that is really the cause, one solution is to modify your wastegate duty cycle in your tune.

It might be related to this:

 

 

 

Although, looking at your logs, you are not overboosting by much I think. But still, the turbo dynamic stuff will kick in if actual is not equal to target. If that is really the cause, one solution is to modify your wastegate duty cycle in your tune.

 

Thanks for having a look! The funny thing is that TD boost Error is showing positive values (slight underboost?) in all the logs, all within acceptable ranges (about 0.5 psi). I'll do another log that includes Target boost later today to see if this is it. One at 50% throttle, and the other at WOT. Would that give a good picture?

 

It certainly FEELS like the sort of "sawtooth" pattern that you described though.

Edited December 17, 2019 by cvince

yeah. maybe log the turbo dynamic variables too, so you can see when they kick in and stuff. Then, try to find a correlation with the sawtooth pattern you feel, by plotting timeseries of the various variables. It may or may not be related.

 

I know in my case it was (and still is to a certain extent). For instance, when I changed turbo and readjusted the wastegate duty cycles, I put too much duty cycle around the rpm range where the turbo was beginning to spool (in the hope of reaching target boost quickly). But then, it always resulted in overboosting at the beginning of the curve. And as I previously said, turbo dynamics kicked in (by modifying wastegate duty cycles) and try to reduce boost as the rpm increased. Resulted in that sawtooth pattern.

 

After fine tuning the wastegate duty cycle, actual boost started to get very close to target boost and that jerky feeling slowly went away.

 

 

We should note that this is different than what most people describe in this thread. I believe they refer to an rpm/throttle plate opening/load ranges where one is still under vacuum and closed loop.

yeah. maybe log the turbo dynamic variables too, so you can see when they kick in and stuff. Then, try to find a correlation with the sawtooth pattern you feel, by plotting timeseries of the various variables. It may or may not be related.

 

I know in my case it was (and still is to a certain extent). For instance, when I changed turbo and readjusted the wastegate duty cycles, I put too much duty cycle around the rpm range where the turbo was beginning to spool (in the hope of reaching target boost quickly). But then, it always resulted in overboosting at the beginning of the curve. And as I previously said, turbo dynamics kicked in (by modifying wastegate duty cycles) and try to reduce boost as the rpm increased. Resulted in that sawtooth pattern.

 

After fine tuning the wastegate duty cycle, actual boost started to get very close to target boost and that jerky feeling slowly went away.

 

 

We should note that this is different than what most people describe in this thread. I believe they refer to an rpm/throttle plate opening/load ranges where one is still under vacuum and closed loop.

 

I don't actually have access to AccessPortTuner. Do you think a low-wastegate map could be used to test this?

yeah, assuming this is the only parameter that is modified in that tune (compared to your current tune). I would surmise that in such a condition, turbo dynamics will try to add more and more wastegate duty cycle until it reaches the max allowable values. So I don't think you'd feel the sawtooth pattern.

I need to say this though: I am NOT a pro tuner by any means!

I need to say this though: I am NOT a pro tuner by any means!

 

So the LWG map helped smoothen it out a smidge. Here are some graphs.... but it definitely still feels like the hesitation is still there.

 

 

It's certainly not a normal feeling by any measure.

I need to say this though: I am NOT a pro tuner by any means!

 

So the LWG map helped smoothen it out a smidge. Here are some graphs.... but it definitely still feels like the hesitation is still there.

 

Without LWG

 

With LWG

 

It's certainly not a normal feeling by any measure.

 

Also attached are the logs. If this is different from what the folks experience on this thread, maybe there's a better thread I can post this in in order to get more opinions.

datalog47.csv

datalog48.csv

Edited December 18, 2019 by cvince
images

I already posted this problem on another thread on this website, didn't realize there was a dedicated thread... sorry. Anyways I bought this car not long ago and somehow this problem never occured on the test drive.

 

TYPE OF STUTTER/STUMBLE

Increasing throttle/Medium to heavy input

 

MODS

Intake: Stock

Exhaust: Blitz NUR spec S axleback

Fuel:Stock

Engine Management: ECU was sent to MINES for a reflash and some other things (Really hoping it isn't an ECU fault $$$!)

Tuner and revision of tune:

 

MAINTENANCE

Sensors changed: O2 sensor with Bosch LS02 (USDM equivalent that was actually avaliable)

Plugs changed: NGK PFR6B equivalent gapped to 0.65mm

Coil packs: Previous owner changed them for aftermarket ones, they looked good and I'll have to pull one out to get the brand and see if they 100% fit on this car.

Air Filter: Changed and good.

 

OTHER SYMPTOMS

CEL: Yes, was given just code 23 for MAF with the black plug test, and given just code 32 (O2 sensor) when i attempted to reset the ECU by connecting green and black conenectors (I fallowed this procedure correctly)

Note: This car was sitting for about a year, and had a near full tank of gas. When I took it home, I barely was limping it up hills the stumble was so bad. It didn't matter how much throttle it was given, the engine still just gave up for a bit (never stalled when this happened, just stopped revving up and the revs fell slowly as I'm waiting with my foot on the gas pedal) it seemed to happen whenever it was given gas.

 

RESULTS

After changing the O2 sensor, my code went away, and the MAF sensor code was just because I pulled the plug out when the car was running to see if that would help (I heard this can eliminate the sensor as an issue on other cars, but the engine died immediately so i guess not on these older subies.

I drained the bad gas as I thought this was the issue, and after cycling a couple tanks with some octane booster and i also tried an injector cleaner, although the stumble was almost never present at low RPM/speed, whenever I gave it the beans, the car stumbled just as hard. I pulled the fuel filter to inspect it and it was disgusting. As I didn't have one on hand, I cycled some fresh fuel through the opposite direction of the filter and blew it through. I have a filter coming any day, and even though I doubt it will fix it, It was certainly time to change the filter.

 

I'm running out of ideas as I have no more hints to fallow since it still stumbles just the same after the O2 sensor change. I was successfully data logging when the car was stumbling, but although I tried to interpret it i realistically don't know what I'm looking at.

Edited July 21, 2020 by kaelanfrost

Fallowup:

 

The car actually stalled for the first time today:(

 

At first the stumble only seemed to happen once the car was warmed up and I've been driving for a while, but the stall happened in the morning when the temp was still climbing. It also seemed to only stumble around the 4000-anything more than that range, but more rarely it stumbles when going from a stop at a traffic light or such. I have to push the clutch back in and give it gas so it free revs up before i can actually get it to move (when it stumbles it feels like the throttle pedal has absolutely no input whatsoever)

 

It is super frustrating to deal with, mostly because I just bought this subie and I want to drive it!!! I still do not understand how no such issues occured on the test drive (it was thorough, through all the gears and up to about 5000, but it was hard to give it all the beans as it was right in the city!)

 

As I do not think ignition is my issue, with newish DP Boosted NP-421 ignition coilpacks (I couldn't find these on their website so a little confused), and brand new properly gapped spark plugs.

 

It feels as if the engine decides that I let my foot off the gas, but it is NOT. I have logged some data, which I can provide a link. If anyone can tell me if something looks off, that would be fantastic.