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The Stumble/Stutter Thread


eightballrj

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Have you done a boost/vacuum leak test smoke test ?

 

I pull the hose off the air filter box, plug it with a pint size paint can, pull the small hose off the blow off valve, give that hose a short blast of air from a compressor, put your thumb over the hose, listen for leaks.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

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Have you done a boost/vacuum leak test smoke test ?

 

I pull the hose off the air filter box, plug it with a pint size paint can, pull the small hose off the blow off valve, give that hose a short blast of air from a compressor, put your thumb over the hose, listen for leaks.

 

This is clever and I will definitely give it a go, but I am 99.9% certain it is not a vacuum leak. My boost logs show 12 on primary and about the same on secondary until it cuts out :/

 

Another thing to note is the cut-out is not at all consistent. Sometimes it at half throttle and 4000rpm, and sometimes it pulls full throttle to 5500 then cuts. All very weird. This makes me think electrical, or a half-broke sensor that freaks out when it malfunctions. Another note is that my gas cap seems to be holding a vacuum in the tank, since when I take it off after driving it gives a ssssss but I'm quite certain it isn't positive preassure as the cap isnt being pushed off when I unscrew it.

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Just chiming in here: I had been complaining about a stutter to my mechanic for a year or more until I, per the recommendation of members here, replaced both AVCS oil control valves. Stutter went away completely for about two days then came back as they got clogged up again. My prior commute to work was three miles and the car didn’t even fully get up to temperature during the drive, which I think made it worse. I’ve since run some Liqui Moly engine flush through the oil and the OCVs are clean again, thus the car drives great until whatever sludge in the oil gunks them up again. I’d notice a decent improvement every time I had an oil change, too, which has led me to change the oil every 1-2K.

 

May not be the source of your problems, but the car will behave so erratically (mine had no CELs either) and it can be hard to trace when these things fail.

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Just chiming in here: I had been complaining about a stutter to my mechanic for a year or more until I, per the recommendation of members here, replaced both AVCS oil control valves. Stutter went away completely for about two days then came back as they got clogged up again. My prior commute to work was three miles and the car didn’t even fully get up to temperature during the drive, which I think made it worse. I’ve since run some Liqui Moly engine flush through the oil and the OCVs are clean again, thus the car drives great until whatever sludge in the oil gunks them up again. I’d notice a decent improvement every time I had an oil change, too, which has led me to change the oil every 1-2K.

 

May not be the source of your problems, but the car will behave so erratically (mine had no CELs either) and it can be hard to trace when these things fail.

 

Good thought. Some of us have learned over the years these cars don't do well when driven for short distances.

 

They need to get the oil hot enough to boil out the contaminants. Those of us that drive the cars for long distances, even 10 miles on the highway have many fewer issues.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

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I'll chime in:

 

2006 Spec B

 

TYPE OF STUTTER/STUMBLE

 

Increasing throttle/Medium input

 

MODS

 

Intake: Stock

Exhaust: full turbo back, GS UP and crosspipe, ported stock header

VF52

New stock injectors and newer sidefeed rails

GS TMIC

TGV deletes

Perrin inlet

Two extra OEM fuel dampers + Radium Eng damper on fuel intake side

Radium Eng FPR

Engine Management: stock ECU

Tuner and revision of tune: Mike at Tuning Alliance + DBW tables revised by me based on Throttlehappy tips from Nasioc

 

 

MAINTENANCE

 

Sensors changed: Bosch O2 sensor few years back

Plugs changed: NGK few years back

Coil packs: OEM few years back

Air Filter: Changed every 5k to newer OEM model (12A)

OCV valves: OEM few years back

 

RESULTS

 

Biggest change had been adding extra OEM fuel dampers to the fuel line, and redone DBW tables to open the throttle plate more at lower RPMs. Now there is zero stutter!

Edited by airgasm
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Just chiming in here: I had been complaining about a stutter to my mechanic for a year or more until I, per the recommendation of members here, replaced both AVCS oil control valves. Stutter went away completely for about two days then came back as they got clogged up again. My prior commute to work was three miles and the car didn’t even fully get up to temperature during the drive, which I think made it worse. I’ve since run some Liqui Moly engine flush through the oil and the OCVs are clean again, thus the car drives great until whatever sludge in the oil gunks them up again. I’d notice a decent improvement every time I had an oil change, too, which has led me to change the oil every 1-2K.

 

May not be the source of your problems, but the car will behave so erratically (mine had no CELs either) and it can be hard to trace when these things fail.

 

 

Can't hurt to try! I'll run some sauce through my oil and see if it can clear anything up! :)

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I'll chime in:

 

2006 Spec B

 

TYPE OF STUTTER/STUMBLE

 

Increasing throttle/Medium input

 

MODS

 

Intake: Stock

Exhaust: full turbo back, GS UP and crosspipe, ported stock header

VF52

New stock injectors and newer sidefeed rails

GS TMIC

TGV deletes

Perrin inlet

Two extra OEM fuel dampers + Radium Eng damper on fuel intake side

Radium Eng FPR

Engine Management: stock ECU

Tuner and revision of tune: Mike at Tuning Alliance + DBW tables revised by me based on Throttlehappy tips from Nasioc

 

 

MAINTENANCE

 

Sensors changed: Bosch O2 sensor few years back

Plugs changed: NGK few years back

Coil packs: OEM few years back

Air Filter: Changed every 5k to newer OEM model (12A)

OCV valves: OEM few years back

 

RESULTS

 

Biggest change had been adding extra OEM fuel dampers to the fuel line, and redone DBW tables to open the throttle plate more at lower RPMs. Now there is zero stutter!

 

As I understand, a fuel damper stops the fuel preassure from occilating too much when the injectors open and releive some of that preassure? So adding extra ones makes it even smoother?

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https://drive.google.com/file/d/1JsVJf7PuN-e2Fa7zvzGikcNXumam0Kmx/view?usp=sharing

https://drive.google.com/file/d/1xxK49MrC1R4_wUeYNu23jhoP5Tcx-EMw/view?usp=sharing

https://drive.google.com/file/d/11JwK2Zxb_mUMOjV7l_-aD7CchVR-yiJI/view?usp=sharing

 

these are some data logs. Cutout only occured in the 3/4 throttle pull as it seems to happen with a more heavy foot, and it happened right before I let off (around the max rpm I acheived)

 

Edit- It didnt name the first log for whatever reason but that one was just primary boost pulls almost to WOT. Also should my Cam position sensor signal be doing that??

Edited by kaelanfrost
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I thought I posted these here before, to fix my stumble between 2400- 3000rpm I "T" the line off #4 intake manifold runner into the hose off the blow off valve. That hose sends a signal to the fuel pressure regulator.

 

Reset the ecu and drive the car.

 

DSCN7339.thumb.JPG.b90bda8459825631b2684e0726d94d67.JPG

 

DSCN7341.thumb.JPG.c019780be51d51da243ce0e1030b4242.JPG

 

The next picture shows stock set up. I took these photo's years ago,

 

DSCN7065.thumb.JPG.1cfe465a65eff4bbf70c63a8c17e4fb3.JPG

Edited by Max Capacity

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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  • 3 weeks later...

Thought it is a good idea to link this thread here.

 

https://legacygt.com/forums/showthread.php/low-load-stumble-totally-lost-282775.html

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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I thought I posted these here before, to fix my stumble between 2400- 3000rpm I "T" the line off #4 intake manifold runner into the hose off the blow off valve. That hose sends a signal to the fuel pressure regulator.

 

Reset the ecu and drive the car.

 

[ATTACH]286103[/ATTACH]

 

[ATTACH]286104[/ATTACH]

 

The next picture shows stock set up. I took these photo's years ago,

 

[ATTACH]286105[/ATTACH]

 

My problem is actually fixed!! I've been having too much fun to write a response on this thread.

 

It turned out to be a faulty fuel pump, as it wasn't building enough fuel preassure for high load situations, and thus fuel cut. I'm not sure why it died, but it did have gas sit in the tank for about a year so maybe that had a role in the failure. It is a super easy fix, just make sure you get the right pump as I heard some replacement ones stick too far down into the tank and hit the bottom! So bottom line, if your car is stumbling HARD when in high load situations, it's either boost or fuel cut from what I've heard, and if you log your boost with ecuExplorer and a vag-com KKL OBD2-USB cable, you can find out if you are lacking boost and if not, give the fuel system a go!

 

This is a link to the pump I used as well as a step-by-step procedure. Even though I didnt need a high-flow pump, I couldn't find many stock ones if any. Hope it's not a crime to link another thread!

 

http://www.uklegacy.com/forums/index.php?/topic/106366-fit-hrc-255-lph-340-fuel-pump-bh5-be5-simple-job/

 

You problably did already post it, I just was done reading through 18 pages of old threads.. but good suggestion!

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This thread needs to be closed.

 

The actual stumble/stutter situation is caused by fuel pressure pulsation created by the factory fuel pressure regulator setup and the location of the pressure reference line to the FPR.

 

COBB has addressed this issue on the plastic intake manifold WRX's and has retrofit kits available that fit the LGT's. There are also DIY fixes that are well documented.

 

Most of the people chiming into this thread have unrelated issues to the original problem.

(Updated 8/22/17)

2005 Outback FMT

Running on Electrons

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I went over to a WRX STI, 2013 and it had the same issue.

 

Here is a great write up by the cobb boys on the problem.

 

At least in the STI world a fuel pressure regulator swap and relocation of the vacuum source did not fully fix the problem. It was better but not altogether fixed.

 

This is what they found.

 

https://www.cobbtuning.com/2008-sti-fuel-pressure-regulator-kit-update-technical-overview/

 

https://forums.nasioc.com/forums/showpost.php?p=43568262&postcount=1

 

After installing the recommended parts mine was rock solid. If I remember correctly I ended up doing lines and rails which got rid of the issue completely.

Edited by Scooby2.5
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I went over to a WRX STI, 2013 and it had the same issue.

 

Here is a great write up by the cobb boys on the problem.

 

At least in the STI world a fuel pressure regulator swap and relocation of the vacuum source did not fully fix the problem. It was better but not altogether fixed.

 

This is what they found.

 

https://www.cobbtuning.com/2008-sti-fuel-pressure-regulator-kit-update-technical-overview/

 

https://forums.nasioc.com/forums/showpost.php?p=43568262&postcount=1

 

After installing the recommended parts mine was rock solid. If I remember correctly I ended up doing lines and rails which got rid of the issue completely.

 

FWIW, the vacuum line T did absolutely nothing for me. I think this thread serves as a good list of potential issues and fixes for the platform. Replacing my AVCS OCVs and doing an engine oil flush solved my stutter, which I wouldn’t have discovered without this thread.

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This thread needs to be closed.

 

The actual stumble/stutter situation is caused by fuel pressure pulsation created by the factory fuel pressure regulator setup and the location of the pressure reference line to the FPR.

 

COBB has addressed this issue on the plastic intake manifold WRX's and has retrofit kits available that fit the LGT's. There are also DIY fixes that are well documented.

 

Most of the people chiming into this thread have unrelated issues to the original problem.

 

Stumble is just a symptom, and more than one thing can cause it.

 

I tried adding a 'water hammer' hose, and that didn't help. It helps some people, but it did nothing for me.

 

I tried moving the FPR pressure source, and that didn't help. This also helps some people, but did nothing for me.

 

Increasing AVCS advanced helped a lot. The factory tune for my 09 has far more advance than the factory tune for my 05, and my 09 never had any issue with stumble/stutter, so I think this approach is under-rated.

 

I've also watched false knock trigger so much timing retard that the car began to stumble in cruise. The stumble in that case was pretty severe. For years I saw threads about this topic and thought people were exaggerating... then it happened to me. Then it happened to me while I had my CarPC displaying IAM, FLKC and FBKC and it was obvious what was going on. I've only had that kind of massive stumble twice in about 90,000 miles, so it's not common, but it's definitely a thing.

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The main issue that this thread is centered around has been diagnosed and known solutions exist. It's not a question if the issue is real or not.

 

This thread should be closed to prevent new people from posting unrelated info that further clogs and disorients people from finding real solutions.

 

There ARE many things that can cause running issues, but a single thread cannot contain all the answers. False knock can be caused by loose heat shields or an old motor with increasing clearances that cause mechanical noise. These are not related to the original content of this post.

 

This thread has become a poop bucket of people's frustrations with little guidance on properly diagnosing and fixing the underlying issues. These cars are becoming old and many are developing problems. This thread is not the first place these people should be looking for help, but many new posters come here for solutions.

 

This thread has become, "Post your issues about your car and hope someone replies with a magical fix."

 

Please close this thread. Force people to actually search instead of adding to the mess.

(Updated 8/22/17)

2005 Outback FMT

Running on Electrons

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  • 6 months later...

08 legacy gt

 

Mods

Perrin turbo inlet and after Maff hose

Cobb high flow catted down pipe

Tomei ARMS MX7960F turbo

Cobb v3 running stage 2 shelf tune checked on with data logs by local tuning shop to make sure things are working well on tune been running this for the last 1.5 years

 

Latest work

 

AVCS system stopped reading on the Cobb changed out avcs solenoids was still not registering on the Cobb put a new oil pressure switch in wham working great so my random shut off problem was fixed. I also installed a new front O2 sensor/ AFR sensor as I was running really rich that fixed that old O2 that I put in last year looked like it got hit by something was dented and the outer Case on the sensor part in the manifold pipe was cracked ran great for two days then last Sunday my boost reading and AFR readings where jumping all over the place

 

Stumble / rough at idle only

 

Boost was jumping from -7.89 to -9.99

 

AFR was jumping from 13.89 to 15.04

 

What I have done checked for boost leaks can't find a single one stumble has gone away but my boost and AFR readings still jumping around at idle

 

Any ideas what could be the culprit possible faulty O2 sensor ? First time I have ever had this issue

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  • 1 month later...

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both:

 

MODS

Intake: None

Exhaust: Catted nvidia DP, Q300 CB

Fuel: 91/93

Turbo: Stock Vf40

Engine Management: Cobb AP V3

Tuner and revision of tune(if you don't mind): Rev2 of torqued performance tune

 

MAINTENANCE

Sensors changed: none currently

Plugs changed: 20 miles ago

Coil Packs changed: 20 miles ago

 

OTHER SYMPTOMS

Check Engine Light: None

Etc: -12 feedback knock around 2300-2500 rpm. Car is pulling timing due to "knock" short block compression and leakdown are fine. No rod bearing material in oil filter.

 

RESULTS

What has and hasn't worked for you: Tried changing from OTS tune to E tune and changing spark plugs and coil packs.

If something worked, how long has it been working for: Nothing currently.

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See post #381

 

I did that years ago. The problem has not returned. Reset the ECU after doing that.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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  • 1 month later...

I stumble and stutter on the way to bed some nights. Usually the cats try to trip me up playing at my feet as I walk. That causes the stumble. The stutter is when I try to "yell" at them to get away without waking the family. It gets worse with a beer.

 

 

Please try the veal, I will be here all week.

 

 

This thread needed a tension break

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try drinking your beer with a coiled up long section of hose - should help the stumble/stutter ;)
BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
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This is on my 1998 Legacy 2.5 (EJ25D, naturally aspirated, 5MT)

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: Both, never at WOT. Only on the highway over 59 mph/~3k rpm and part throttle.

 

MODS

Intake: none

Exhaust: uel header, tsudo high flow cat

Fuel: none

Engine Management: stock, with a grounding kit and big 3 kit

Has STi Group N engine, dogbone, and transmission mounts

 

MAINTENANCE

Sensors changed: Upstream O2 with a Denso, and ECT with OEM about 5 years ago, MAF cleaned at the same time. MAP swapped with known good one off my other Legacy that does not have this issue, no change. Knock sensor replaced with OEM about 3 years ago, torqued and angled according to FSM instructions. CKP, CMP, and TPS are all original.

Plugs changed: NGK laser platinums, 42k on them

Coil Packs changed: MSD 8239 coil pack, 33k on it. Wires are NGK blue with about 25k miles.

 

OTHER SYMPTOMS

Check Engine Light: Rarely ever throws a CEL while stumbling. The couple of times it did, it had misfire codes on all 4 cylinders. Right before it started stumbling it was throwing an EGR Flow code (P0400) at about 50-55 mph in 5th, and weirdly not since despite no parts replaced except all the small diameter rubber vacuum hoses in the engine bay as they were old and hard, which did not make it stop throwing the EGR code.

 

RESULTS

What has and hasn't worked for you: Noticed header was cracked in front of the upstream O2 possibly causing false air readings, replaced it today along with all associated gaskets. It behaved for the initial test drive, but I drove it again later today and it did it again. Putting 87 octane gas instead of my usual 89 made it slightly less worse but that could be a red herring.

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