The Stumble/Stutter Thread

[Volta55]

I might as well sub myself to this thread, although I have been advised through Max Capacity and Tuning Alliance.

05 LGT auto bought 2 weeks ago

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TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both: 20-35mph in the 2-3K RPM range ( like following a slow-poke going up a hill ) and if i downshift to get out of the studder, it jumps into 2nd and takes off like a rocket

 

MODS

Intake: K&N Panel filter

Exhaust: stock

Fuel: Stock fueling, 93 octane

Turbo: stock

Engine Management: stock

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

 

MAINTENANCE

Sensors changed: going to clean MAF

Plugs changed: none

Coil Packs changed: none

 

OTHER SYMPTOMS

Check Engine Light: none

Etc: slight shaking/vibration at a dead stop with foot on brake ( maybe its just a Subaru thing, my dads 03 legacy does the same )

And 18 MPG combined highway/city :/ ( even on a long 2.5 hour drive up to the catskills and back, with no bike roof or anything on roof, got a max MPG of 22 )

 

RESULTS

What has and hasn't worked for you: all random. today driving from apartment to family lunch it did not do it at all ( merging onto highway, etc ) I am at a 1/4 tank with 93 octane ( was much worse a couple days ago with more fuel )

If something worked, how long has it been working for: using the auto/manual option to keep rpms at or higher than 3K to avoid the "studder range" to get up hills. once I am moving at highway speeds, all is well.

 

I understand I need a full day of looking over and under the motor and checking out the fuel delivery and spark delivery systems, but it just confuses me that sometimes it drives just fine, which makes me feel like its a ECU problem.

 

I am considering getting aftermarket UP and DP pipes and having my ECU tuned my Tuning Alliance, but before i spend that money I want to see if i can fix this myself ( is that even possible? )

[Volta55]

We have seen many different versions of the "stumble". We have come across many different fixes.

 

For some it is a slight vacuum leak. Post turbo.

 

For some it is a dirty MAF.

 

For some it is a dirty or faulty TPS. In older cable TB cars it was the idle air solenoid.

 

For some it is a front (A/F) O2 sensor that is reading off.

 

For some it is a leaking BPV (leaking to atmosphere).

 

It can be a total mystery when combined with 5EAT's too.

 

 

going to try this as well... thankyou

[mwiener2]

Anyone try the Fuel Pressure Regulator tricks like the 08+ Impreza guys have been doing for their "stutter" issues?

[MTBwrench]

Anyone try the Fuel Pressure Regulator tricks like the 08+ Impreza guys have been doing for their "stutter" issues?

 

Are you talking about a direct supply with an STi regulator on the return line?

[Volta55]

few things I am noticing

 

i drove about 300 miles in "manual mode" for shits and giggles (I have a 5EAT) shifting at around 4/ 4.5K

 

After putting it back into normal auto or sport auto mode, I am currently not getting any studder in the low rpm range.

[NSFW]

I have a hunch that's correlation, not causation. See how long it takes for the stumble to come back...

[WRX USA]

Anyone try the Fuel Pressure Regulator tricks like the 08+ Impreza guys have been doing for their "stutter" issues?

 

I'm curious about this as well.

[Volta55]

I have a hunch that's correlation, not causation. See how long it takes for the stumble to come back...

 

 

aaaand it lasted not even a day

 

staying in "manual" mode until i can figure this bullshit out

[Redslaya]

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both:

Idle drops and whole car vibrates when stopped on an decline and sometimes on an incline. stopped on flat ground idle is fine. goes away once on the throttle both steady, accelerating, and WOT

 

MODS

Intake: Stock Intake

Exhaust: 3" turbo back catless unresonated

Fuel: Shell 93

Turbo: VF40 stock

Engine Management: Stock ECU, accessport

Tuner and revision of tune(if you don't mind): OTS stage 2

 

MAINTENANCE

Sensors changed: none

Plugs changed: few months ago

Coil Packs changed: Little over a year ago

 

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:

[Redslaya]

double post

[flip213]

You asked Cobb for advice. They gave it. You have not followed it, yet now you ask for advice here.

 

If you dont want to take the advice, dont ask for it.

 

Compression and leak down check. Your "stumble" is not what is being cataloged in this thread. You have a mechanical issue that was not there before. Something has physically changed. Cobb gave you good advice.

 

Iridium plugs are supposed to last 60000 miles. But you say you are not misfiring, so it should not be plugs. As plug gap just begins to get too large, you should experience a misfire at the top of the RPM range under WOT.

 

M_sprank

 

I did not take Cobbs advice because if my problem truly was a compression issue then i would losing power and the engine would be also idling erratically, i've seen compression problems before and mine definitely wasn't it. Also it would be a progressive decay. My stumble happened from one day to the next.

 

So to let everyone know on this forum i have found my problem, a while ago, but have not had the time to respond to this thread. It was my fuel pump not delivering the correct fuel pressure (tired pump).

 

Check the fuel pressure you are getting from your fuel pump, the manual states you should be getting 41-46 psi from the fuel delivery hose after the regulator at idle with the vacuum hose disconnected and 33-38psi with vacuum hose connected.

 

I was 6-7psi below the spec. Bought a new deatschwerks D65C pump and stutter is gone and i've noticed stronger and much smoother acceleration.

[m sprank]

Your post gave me a good chuckle. Thanks.

 

Glad you found your issue and was able to resolve it.

[acdcrockme]

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both:Both at 10psi

 

MODS

Intake:stock

Exhaust:stock

Fuel:94 octane

Turbo: ihi vf33 and ihi vf33

Engine Management: stock

Tuner and revision of tune(if you don't mind): stock 99 b4 rsk rev b

 

MAINTENANCE

Sensors changed: none

Plugs changed: none

Coil Packs changed: none

 

OTHER SYMPTOMS

Check Engine Light: no

Etc:

[acdcrockme]

TYPE OF STUTTER/STUMBLE

Steady throttle/Increasing throttle/Both:Both at 10psi

 

MODS

Intake:stock

Exhaust:stock

Fuel:94 octane

Turbo: ihi vf33 and ihi vf33

Engine Management: stock

Tuner and revision of tune(if you don't mind): stock 99 b4 rsk rev b

 

MAINTENANCE

Sensors changed: none

Plugs changed: none

Coil Packs changed: none

 

OTHER SYMPTOMS

Check Engine Light: no

Etc:

[mwiener2]

Do this https://www.rallysportdirect.com/part/fuel-pressure-regulators/cob-315200-cobb-tuning-fuel-pressure-regulator-kit

 

Fix studder.

[m sprank]

Yup.

 

$300 to replicate what I have been installing for local customers for over 3.5 years. I sell mine for $50. Extending the fuel lines and supplying manifold reference to the FPR from the entire manifold, not just a single runner works wonders.

 

Now that Cobb sells it I guess my fix is "proven". Lol.

 

Hows Colorado treating you Mr Wiener? Hope all is well.

[NSFW]

I'm puzzled as to why that kit would require tuning.

[Volta55]

I have been avoiding normal D mode ( I have an auto ) and even sport mode sometimes; I have been driving in nothing but semi-manual mode and i do not have the water hammer effect.

 

but when I do it stumbles.

 

I would love to buy your kit, @m_sprank , but I do not have a tune.

[utc_pyro]

I'm puzzled as to why that kit would require tuning.

 

They want you to tweak the load compensation tables. Presumably you'd want to do this on the '05-'06 legacy as well, though our table cuts off at 2000 rpm.

Edited March 24, 2017 by utc_pyro
Typo

[m sprank]

You dont have to tune. the mechanical changes take 90% or more of the issue away. You can adjust load compensation as well as learning adjustment in the effected ranges to eliminate it 100%. Many customers decide to just modify the plumbing without a tune adjustment and are more than satisfied with the results.

 

You need a few feet of 5/16" fuel injection hose (I prefer Continental) and the associated 5/16" quick disconnect fittings (to a barb so you can clamp to the line) and the fuel hose clamps. Then you need some vacuum hose (I prefer silicone) and a "t" (I use the tees provided by Turkeylord). Its scary basic, but works.

[1SIKLGT]

Yup.

 

$300 to replicate what I have been installing for local customers for over 3.5 years. I sell mine for $50. Extending the fuel lines and supplying manifold reference to the FPR from the entire manifold, not just a single runner works wonders.

 

Now that Cobb sells it I guess my fix is "proven". Lol.

 

Hows Colorado treating you Mr Wiener? Hope all is well.

Interested in purchasing this kit.

 

Sent from my LG-D725 using Tapatalk

[m sprank]

Its not a "Kit", LOL. Its what I do for customers at my shop.

[turk56]

Adding another case to this list, hoping someone can point me in the right direction.

08 Legacy 2.5i Special Edition, 160kmi.

 

Symptoms: very hard to start, stutters and stalls when coming to a stop in traffic (will not stall if I shift into N and give it some gas to keep the RPMs up). CEL stays off even when it stalls out, but recently had a misfire code in Cyl 3. When idling, if I barely touch the accelerator, the RPMs drop to about 400 and that is when the shaking starts. Other than that it idles fine.

 

What I've Tried: ran a can of seafoam through the last tank of gas to hopefully clean up any injector issues; changed spark plugs (it was due anyway). No help with either.

 

Concerns:

- Could this be the fuel pump going out?

- Coil pack

- Bad injectors

- What else?

 

Maintenance: new plugs at 80k, 160k; timing belt at 100k, all other belts at 120k, regular oil changes, no mods.

 

Any help here would be hugely appreciated!

[utc_pyro]

I zeroed out the MAF load compensation table this afternoon and things got MUCH smoother at idle and low load. That said, I don't think "zero" is the correct answer, there was still a lot of fueling compensations happening but it was subjectively smoother.

 

fahr_side has a post about actually tuning this table, and empirically it appears Cobb's suggestion to tune if you screw with the FPR or it's reference is quite valid.

 

My system is simular to the STI fuel pressure regulator/sti pulse damper setup but using Radium parts.

[NSFW]

I moved my FPR's pressure signal from the intake runner to a T in the BPV hose today, and it made a big difference. I'm not sure it solved the problem 100% but it's pretty close. My car is lowered on 18s with slightly stretched tires (225 on 8") so it's kinda hard to tell whether the remaining roughness is just the road or still the motor.

 

I've tried a bunch of other things in the past (load compensation table, 20" T off of the fuel line, fuel line dampers...) but nothing else fixed the intermittent roughness while cruising in the 2000-2500 RPM range.

 

I'm going to try the same thing on my OBXT next, as it has a similar problem. Being 5EAT, the roughness is somewhat damped out by the transmission, so it took me a while to be sure I wasn't just imagining it. But on the other hand, it's a got a smooth ride so I'm expecting it to be very smooth after this. My next couple weeks are going to be really hectic though, so it might be a while before I make the change.