The Stumble/Stutter Thread

Just got the stumble back after a harsh winter of below zero temps accompanied by a p2096 cel FML

 

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Not had time to log yet, however did notice Drive vs Tiptronic made no difference when I tested it up a hill on way home from work tonight, thrashed it in D and it stumbled yet again. Also tested in 'I'ntelligent mode but ran out of road lol. What a waste of a mode I is. S or S# only!

Well the transmission (or rather TCU) has just been completely ruled out... I just met up with stibbutt and went for a drive in his 5MT legacy - he has EXACTLY the same issue. He had local tuner do his tune (unsure what 'stage'), but no DP (doh) just a k&n panel filter. His stumble is more abrupt and also happens around the 5,000rpm mark. According to his tuner a fuel cut to protect the turbo? As a separate issue his IAM is at about 0.375 too (all other LV figures are fine) Told him to try 98 octane (95-ish USA equivalent) which he's done just short of 100 miles on and no change. My IAM sits at 1.0 quite happily, all other LV fine too. Gotta be a tuning parameter somewhere I'm sure.

There isn't really anything in the ecu that would tell the car to cut out at a specific rpm for a second and then continue through the rev range. The other thing to keep in mind is that this issue was not always present, it came and went throughout the tuning process which kind of eliminates the hard coding as an option unless its in some compensation map based on temp etc. The fact that its not throwing any lights means that its not tripping any factory limits set in the ecu as a fault code either.

 

A fuel cut to protect the turbo? not sure what he would be getting at there but an IAM at .375 would have me concerned regardless.

 

Go ahead and send me an email like I mentioned and we can take a look at a few things. The fact that it happens on two 100% different tunes on different cars with different tuners/transmission types/mods etc makes me scratch my head as there are not a lot of common driving factors there.

 

Talk to you soon.

 

Dave

Go ahead and send me an email like I mentioned and we can take a look at a few things. The fact that it happens on two 100% different tunes on different cars with different tuners/transmission types/mods etc makes me scratch my head as there are not a lot of common driving factors there

Exactly! That got me kinda happy because 1. I was not alone and 2. it ruled out my transmission and 3. we can potentially run logs on both cars and do some comparisons (when he's back to IAM 1.0 of course)

 

Both car's are 2008 LGT's (JDM), however his is spec B manual mine is non-spec B tiptronic (not that spec B should make any difference) Will be interesting to see what turbo he has too, from memory mine was VF44. His IAM is crap for sure, and thats something he will need to work out first. I will find out if he has a copy of his stock ECU and perhaps remap back to stock and try it out. Will also see if I can get him to take it to the mechanic and check for sure if he has an aftermarket DP installed (unless there is any easy way of telling? at a glance I couldn't tell)

 

Sorry haven't got the logs to you yet - every night there has been something on... got the kids tonight as the wife is out... beer o'clock...

Thoughts...? What interests me is "Yes, the stuttering issue has since been fixed. Stage 1 helped a LOT! Stage 2 was even better, and it is pretty much gone with a PDX e-tune." I feel that the stutter on the stage 2 tune by cryo is "less abrupt" than at factory

 

http://legacygt.com/forums/showthread.php/2009-lgt-massive-stutter-95302p3.html

 

http://legacygt.com/forums/showthread.php/stutter-fix-2009-lgti-11-87-08r-125156.html?t=125156

I think the studder that is mentioned by most others is not what your experiencing. Mist have a slight studder at standard cruise, yours is during hard acceleration.

 

Just shoot me an email when you have a chance,

 

Dave

Might it be going lean at that point? Not sure if you were logging the front o2 or not(?) Haven't seen the logs.

I've emailed my logs to Dave after a few runs late last night. I did notice when the studder happened, the boost gauge (which I've just installed) showed boost dropped from 18psi to 13psi within a split second.

 

I will do another test tonight where I'll go hard on acceleration through 2nd as per usual, change into 3rd but just before around the 5,000rpm's (where it stumbles) I'll ease off and pull through the rev range a little less aggressively and see if it still does it. Need to see if its just in WOT or if the ECU balances shit out if I ease into high rev's when hitting 3rd. Its almost as though the fuel pump can't keep up with the rate of gas being consumed - like a complete cut to the injectors for a split second. PITA and getting a little pissed off with it now.

could be going lean and the sudden lack of power would cause boost to drop. conceivable...

 

but if the boost drops very suddenly, it could be blowing open the bpv, or blowing open the wg, or sucking the tih closed, etc. u running stock tmic?

Yeah bro, stock tmic

 

 

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TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: 2200rpm stutter, feathering gas prevents it.. Zero stutter on stock tune, didnt begin until I flashed a Cobb Stage1 through AP, goes away completely if I revert to stock tune.

 

MODS

Intake:

Exhaust:

Fuel:

Turbo:

Engine Management: Accessport

Tuner and revision of tune(if you don't mind): Cobb Stage 1 AP v1

 

MAINTENANCE

Sensors changed: no

Plugs changed: no

Coil Packs changed: no

 

OTHER SYMPTOMS

Check Engine Light: yes, p0011 (removed banjo filters)

Etc:

 

RESULTS

What has and hasn't worked for you: Removing the tune works

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

I have some questions for the people still having this issue after all this time:

 

1. Are you using the stock or aftermarket intercooler?

2. Which brand and grade gas are you using?

3. Which Oil are you using?

4. Geographically speaking, are you on the East coast or West coast?

Sub'd to read through later.

1. Are you using the stock or aftermarket intercooler?

2. Which brand and grade gas are you using?

3. Which Oil are you using?

4. Geographically speaking, are you on the East coast or West coast?

on stumble, logging shows wgdc and timing drops to zero and idc drops from 75 or so to 2.85. watching boost gauge, psi drops from 18 to 12 in a split second. its like a total fuel and boost cut. heiche is possibly right, in that its going lean and cuts out - possibly intermittently inaccurate sensor voltage or mechanical issue, maybe actuator or bpv does get stuck. who knows. what's bizzare is it doesn't always happen - letting the car shift from 2nd to 3rd, or from 3rd to 4th sometimes happens, sometimes doesn't (generally won't happen if it shifts up and is above 5,200rpm's, if shifts and slightly less than 5,000rpm's, it'll stumble). I can replicate it every time if I shift myself though (tiptronic), slightly before redline (so rev's on the up shift are < 5,000rpms). anyways, dave @ cryo is onto it and analysing logs right now - I have utmost faith in him! Edited March 10, 2014 by chimera

TYPE OF STUTTER/STUMBLE

A consistent stutter/stubmle (loss of power) while accelerating or cruising through/at 2500-3000RPM.

 

MODS

Intake: KSTech 73mm CAI

Exhaust:Killer B ELH, Invidia 3" DP, Nameless Performance CBE

Fuel: 93 oct, DW 65c, ID Topfeed 1000cc Injectors, T1 Topfeed Conversion Rails/Lines (Plumbed in Series)

Turbo: Dom 1.5 XT-R

Engine Management: Open Source Dyno Tune

Tuner and revision of tune(if you don't mind): Keith Fields, first.

 

MAINTENANCE

Sensors changed: Yes

Plugs changed: Yes

Coil Packs changed: Yes

 

OTHER SYMPTOMS

Check Engine Light: No

Etc:

 

RESULTS

What has and hasn't worked for you: N/A

 

If something worked, how long has it been working for: While tuning, Keith was having difficulites tuning due to the stumble/stutter around 2500-3000RPMs. The results were inconsistent between dyno pulls. He was sure it was a leak somewhere. But a pressure test proved a leak to not be the issue. As a last ditch effort, we replaced the OEM Fuel Pressure Regulator/Assembly (Regulator and dampener) and installed an 06 STi Fuel Pressure Regulator. After doing so, the stumle/stutter was no longer evident and Keith was able to continue on with the tune. It's only been a few days, but no stutter/stumble issues.

Edited March 17, 2014 by Benjamin M

TYPE OF STUTTER/STUMBLE

A consistent stutter/stubmle (loss of power) while accelerating or cruising through/at 2500-3000RPM.

 

MODS

Intake: KSTech 73mm CAI

Exhaust:Killer B ELH, Invidia 3" DP, Nameless Performance CBE

Fuel: 93 oct, DW 65c, ID Topfeed 1000cc Injectors, T1 Topfeed Conversion Rails/Lines (Plumbed in Series)

Turbo: Dom 1.5 XT-R

Engine Management: Open Source Dyno Tune

Tuner and revision of tune(if you don't mind): Keith Fields, first.

 

MAINTENANCE

Sensors changed: Yes

Plugs changed: Yes

Coil Packs changed: Yes

 

OTHER SYMPTOMS

Check Engine Light: No

Etc:

 

RESULTS

What has and hasn't worked for you: N/A

 

If something worked, how long has it been working for: While tuning, Keith was having difficulites tuning due to the stumble/stutter around 2500-3000RPMs. The results were inconsistent between dyno pulls. He was sure it was a leak somewhere. But a pressure test proved a leak to not be the issue. As a last ditch effort, we replaced the OEM Fuel Pressure Regulator/Assembly (Regulator and dampener) and installed an 06 STi Fuel Pressure Regulator. After doing so, the stumle/stutter was no longer evident and Keith was able to continue on with the tune. It's only been a few days, but no stutter/stumble issues.

 

 

 

 

Did you ever rewire the fuel pump?

 

2 big threads on the forum about it and I was one of the ones to discover the undersized wiring feeding the fuel pumps on the legacy.

I had all the supplies to do so and intended on it, but due to some delays, there wasn't time for both wiring install and dyno/road tune, so I picked the latter.

 

 

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Just remember your AFRs and injector duty cycle will change once you do it.

Just remember your AFRs and injector duty cycle will change once you do it.

 

 

Thanks! My tuner suggested that when I get around to upgrading the wiring, FPCM, and an aftermarket FPR, that I plumb the new fuel lines in parallel. He's seen that aid many if his customers stumble problems.

 

And we'll revise the tune accordingly.

 

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I wanted to add my experience on my 2008 5EAT Legacy GT

 

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: Steady throttle creates a hesitation/surging effect while accelerating

 

MODS

None- bone stock

Stock Intercooler

 

GAS/OIL

93 Octane Speedway Gas

Subaru 5W-30 Synthetic

Ohio (midwest)

 

MAINTENANCE

Sensors changed:

• Changed out OEM front O2 (oxygen) sensor for Denso model. Denso model caused engine to throw P0131 & P0134 codes.
  
• Then had dealer change out Denso model O2 sensor for OEM O2 sensor
  

Plugs changed: No

Coil Packs changed: No

 

OTHER SYMPTOMS

Check Engine Light: P0131 & P0134 codes on Denso sensor only. Stock (faulty) OEM sensor gave NO codes!

 

RESULTS

What has and hasn't worked for you:

As mentioned above, I was experiencing a surge/release when holding the accelerator pedal steady between 2500-5000 RPMs. I suspected the O2 sensor was faulty in my car and swapped out the stock sensor (87k miles on it) for a Denso direct-fit replacement from advance auto parts. It should be noted that my stock sensor did not throw any check engine lights or codes. However, once the Denso sensor was in, the car would drive without a code for a while, then stumble/stutter/surge and then immediately throw P0131 & P0134 codes (and subsequently drive fine in open loop mode). I decided at that point to have my dealer take a peek at it. They swapped out the Denso sensor for an OEM O2 sensor. So far no surging and no check-engine lights or codes. Additionally, my dealer also found a vacuum leak near the recirculation valve at/near "a bolt". They previously also replaced my "air intake boot underneath my intake manifold" which was damaged/cracked. The combination of the above seems to have fixed my problem and I am no longer contemplating trading in this car.

 

If something worked, how long has it been working for: About 24 hours. Will update again as time goes on if anything changes.

 

Update: Almost 2 weeks later its still running great and no stutter!

Edited May 8, 2014 by Meltdown07

TYPE OF STUTTER/STUMBLE

Increasing throttle

 

MODS

Intake: KN Filter

Exhaust: gruppve vs headers, sti Uppipe, invidia downpipe, OEM catback

Fuel: walbro fuel pump

Turbo: PDX turbo, 18g

Engine Management:PDX tune by Jarad

Tuner and revision of tune(if you don't mind):

 

MAINTENANCE

Sensors changed: none

Plugs changed:none

Coil Packs changed:none

 

OTHER SYMPTOMS

Check Engine Light:none

Etc:

 

RESULTS

What has and hasn't worked for you:

If something worked, how long has it been working for: about a year with the stumbling that got progressively worse.

 

Got to work on my friends 05 legacy wagon again as he had an Uppipe leak with turns out the Uppipe broke in half. After replacing it with a 2014 WRX OEM catless Uppipe, and doing some maintenance like replacing driver side axle due to torn CV boot for who knows how long, I went about the stumbling problem.

 

The stumble was really bad from a standstill or rolling start, occurred in reverse speed as well so at first I went about cleaning the KN air filter in the OEM airbos which was filthy. Problem still occurred.

So I figure I go check for vacuum leaks and traced it to a heat damaged, crumbling vacuum hose going to the turbo wastegate. Replaced it with a silicone vacuum hose I had laying around in my tool box and stumble went away.

On the test drive I did through a Cel or engine light, so I'm going to check it out, but at least stumble is gone. Not sure why the Cel code, as everything was working fine before, but hopefully its something easy to fix and clear.

abakja1, have you tried pulling the K&N and replacing it with a paper or non-oily filter?

 

After you pull it, be sure to clean your MAF well as it's likely coated in the stupid oil they use on the K&N

TYPE OF STUTTER/STUMBLE

Steady throttle: Steady slight stumble at idle. Car has stalled in slow traffic and one time in parking lot with car in drive and foot on the gas(simulated traffic).

 

MODS

Exhaust: SPT cans and CNT Highflow Cat DP

Fuel: 93

Turbo: VF52

Tuner and revision of tune(if you don't mind): Road Tune

 

MAINTENANCE

Sensors changed: Rear O2

Plugs changed: OEM

 

OTHER SYMPTOMS

Check Engine Light: Rear O2 sensor (P0420)

 

RESULTS

What has or hasn't worked for you:

Carb cleaner tested vacuum lines/Intake Mani/Injectors, Cleaned MAF sensor, Changed air filter, SeaFoamed fuel system

Replacing the O2 sensor removed P0420

 

Timed the car to get a better sense of when things were happening. The timeframe below happens each time(0:00 to 4:40).

 

Started timer

0:30 Almost stalled twice(had batt unplugged)

3:56 Almost stalled/big stumble

4:30 Started hunting for idle (possibly from entering closed loop)

4:40 Slight stumbles are constant/no code/rpms remain at a constant 800

18:00 Carb cleaner tested vac lines, intake manifold, and injectors(no _______change in rpm

25:00 Shut the car off

 

Drove the car for well over 30 minutes. Gave her the beans and everything. Power is all there still. Stumble is felt during low idle, i.e. sitting in parking lot or slow traffic. Low on funds right now so can't really get it diagnosed. Possible front O2? Gunked up throttle? I can at least afford a nother bottle of Seafoam for the intake. Any other ideas for an empty wallet guy?

Anyone try the fuel line or fpr modifications the newer wrx's have been doing?

 

 

http://www.cobbtuning.com/products/fuel-system/subaru-fuel-pressure-regulator-kit-sti-2008-2016