The Stumble/Stutter Thread

Update: I cleaned my throttle body and no improvement

 

Damn

 

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I remember catalyst had a very similar issue and it turned out to be his silicone intake collapsing at about 5200rpms causing a huge power surge like you describe.

 

The TCU thing is interesting based on what we were seeing with the weird rpm behavior during the pulls.

 

Dave

Thanks Dave. After clearing the TCU code, went for another test run and again - it happened. Its most noticeable up hills - flooring in 2nd then into 3rd, about 4900 rpms this time. Didn't think about the intake side but does make complete sense - I'll check it out and see if there is anything obvious, thanks.

good idea! have you noticed any increase in nvh? any pics?

 

I used to get the fuel line vibration in the driver dash area sometimes.... now I get it almost all the time.

 

No pics. It looks like stock but with some goo mushed into it.

I used to get the fuel line vibration in the driver dash area sometimes.... now I get it almost all the time.

 

No pics. It looks like stock but with some goo mushed into it.

 

i see, thanks. did you drop the ds, or manage to accomplish it in place?

I took it out. It really should cure at least 2 full days before using

I remember catalyst had a very similar issue and it turned out to be his silicone intake collapsing at about 5200rpms causing a huge power surge like you describe

Actually the more I think about this, the more sense it makes. I was chatting about this to another guy who used to have a Nissan skyline and he was saying its exactly what happened to him. He cut the intake hose in half, put an aluminium sleeve inside and clamped it back together and never had a problem since. I went down and popped the bonnet and squeezed the pipe, I'd come back from lunch an hour prior - yet the pipe was still soft and squeezed together pretty easily. I'll try this in the next few days and report back. Thanks for the heads up Dave!

I've seen a turbo explode from an intake snapping shut at high rpm. Bad bad bad.

I've seen a turbo explode from an intake snapping shut at high rpm. Bad bad bad.

ouch.

 

I cut the rubber pipe last night and put in a piece of PVC piping the same diameter then taped it up and went for a drive. On first tests, it appears to have fixed the issue. Obviously I don't want this to be a permanant solution, so what after-market pipes are available to fit here? Thanks

TYPE OF STUTTER/STUMBLE

Increasing throttle, lower RPM hesitation. Really bad when cold, car will struggle to even accelerate. Whats weird is sometimes the AFR A,B,C, D will sometimes change depending on the ECU reset....

 

MODS

Intake: Stock

Exhaust: Grimmspeed uppipe, gutted down

Fuel: Chevron 92

Turbo: Stock

Engine Management: AccessPort V3

Tuner and revision of tune(if you don't mind): Cryo, rev5.

 

MAINTENANCE

Sensors changed: MAF, O2, Knock

Plugs changed: About 2K ago

Coil Packs changed: No

 

OTHER SYMPTOMS

Check Engine Light: No

Etc:

 

RESULTS

What has and hasn't worked for you: Tried many things. Replaced MAF, fuel pump, O2 sensor, knock sensor, throttle body cleaned and new seal, stock intercooler pressure tested and new O rings, Pressure tested system as a whole, tested no leaks. Tested again today actually, and again no leaks. Removed MAP sensor filter. Compression is perfect 145 on all cylinders. Driving yesterday I was pulling -7 on Learning 1D, and when I hit that MAF flow range the car would stutter also. Re set the ECU again and now its back at 0 after driving around. Today left for lunch, and the car hardly ran until it was warmed up, I got like 34 counts of knock, timing pulled like crazy. Re set ECU and drove back to work, perfect, no knock.

 

If something worked, how long has it been working for: Nothing, driving me crazy. Thinking of trying OCV I guess. Ugh this is a money pit.

Edited November 25, 2013 by Brian3676

Brian3736 - a large negative number in the D trim indicates a leak or rich conditon during boost on set. things like a leaking intercooler or other places that boost could escapeafter its already been metered. With your car being pretty much stock it limits the things that could cause this

 

Dave

Yes I know, and at idle it adds about 1.56, indicating a leak also, positive under vacuum, negative under boost. I am getting really frustrated trying to find it. I have done about 5 boost leak checks, even using some really fancy expensive foaming solution I got from work we use to find leaks. I re set the ECU, and now only have slight correction at idle. I don't under stand why I can re set the ECU and my corrections will be different every time. I am thinking of doing the OCV's. Might do the intake gaskets again though, even though I have no foaming from the solution under pressure, or idle change when starter fluid is sprayed.

 

I am still going to get the MAP revision from you Dave for the downpipe, I just want to have this straightened out first! On a side note, I noticed that my MAF scaling was changed, even though I have a stock intake. Is this common? Or a sign the new maf I got could have been bad?

The idle fueling has been adjusted slightly to get it to stay in range but it was not far off. That's the reason for some of the maf adjustments as they are not always perfect from the factory and I like to hone them in a little closer. The factory allows about a 7% to 9% variance and still considers it "in line", I like to get them much closer.

 

Its hard to say whats causing your "studder" in this situation since you have checked the common issues and your car is stock for the most part.

 

I just sent you an email as well.

 

Dave

I've been dealing with this problem too.. Took it to a local tuner that uses rom raider and he was going to see if he could tune it out but no luck .. I cleaned maf and changed plugs nothing, still does it! Mine does it when my car is totally warmed up only! I noticed if I drive for less than 20 min it doesn't happen. Over 20 min it happens right when you push on the gas pedal at times. No cel ever for me.

Actually the more I think about this, the more sense it makes. I was chatting about this to another guy who used to have a Nissan skyline and he was saying its exactly what happened to him. He cut the intake hose in half, put an aluminium sleeve inside and clamped it back together and never had a problem since. I went down and popped the bonnet and squeezed the pipe, I'd come back from lunch an hour prior - yet the pipe was still soft and squeezed together pretty easily. I'll try this in the next few days and report back.

Unfortunately altering the intake to stop it 'collapsing' did not resolve the issue. I took it for another test run and again, almost exactly at 5,000rpm's in both 3rd and 4th it stumbled for a split second (even though its very short, it really feels bad and I hate to keep doing this to test it). Interestingly though, LV does now show 2 x CEL's, a P0102 (MAF Sensor Low Input) and a P0113 (IAT Sensor High Input). Should I be cleaning the MAF sensor? Any ideas? Thanks.

I have been trying to find the low RPM, light throttle hesitation/stumble issue on my car. I have been logging everything I can. OCV's, cylinder roughness, knock ect... It its NOT pulling timing, or getting any knock when it happens, in fact everything logs perfect. The only thing I have noticed is that it does it on closed loop, and clears up just after swapping to open loop, its almost like there is 2 things fighting with each other over who is right. MAF vs O2? But both are brand new.....

 

Sent Dave (cryo) an e mail for suggestions since he is always very helpful. I also have an apt to get the car smoke tested today since when I boost leak test I find 0 leaks.

I doubt you'll find anything with a smoke test. I thought that was my problem too and found nothing at all. I currently have the stumble on my maf tune. switching to an sd tune helped but moved it to a lower rpm. And FWIW i have it on closed open loop transition also. The only thing that I have found that cures this type of stumble is press the gas more to make it completely transition over. I'm about to swap over to the 07 sti fuel rail/fpr setup and see if it works like it does for the GR stumble.

Ended up being a insanely small leak in the stock intercooler. I was amazed a leak that small would cause such a big issue, but once I replaced it and Dave at cryo re did my map the car is amazing.

so you did find a leak? I couldn't find a leak at all and i still had the stumble after tons of leak tests. I'm running 1000cc injectors and the 65c dw fuel pump so that is normally when people start to see stumbles on most subarus. Glad it worked out for you. I'm going to a different fuel rail setup to see if it cures my stumble. When I was running 750cc injectors and a vf48 I had no problems. The only things that changed on my setup was the turbo, injectors, and header. I'm guessing the bigger injectors are what did it. The sd tune helped a ton with the stumble but I'm still not out of the woods yet. Edited January 3, 2014 by jakesurfin

I did yes. I did proble 5-6 boost leak tests and never found anything. Even used this foaming solution I got from my work that's basically $50 soap and it never foamed where I could see. Got a smoke tester and found a very very small intercooler leak where the end tanks separated just slightly. My car is mostly stock tho, so only so many issues it could be. Yours has a lot more done to it so maybe it's not something so simple.

Been a while since anyone posted in here. My car has been doing awesome. Still had a very very faint hesisitation at 2500-3k rpm's if I was cruzing at a constant speed then went to lightly accelerate. Was board and playing online and read about someone saying it was there rear o2 sensor. I went into race tuner and disabled my rear o2 sensor, and is far it seems as though the issue is gone! Anyone else try this or have an opinion about doing it? One confusion I had, is if the ecu uses the rear o2 to help with the afr in closed loop, and I don't have a cat, wouldn't that mess it up? It's tuned to listen to the rear o2 based off there being a cat there, now there is not.....

I'm still having issues with this. In 3rd or 4th gear, around 5000rpm's, stumbles (or feels more like a complete cut out) for a split second. Interestingly if I floor it in 'D'rive then it doesn't seem to do it (because when it shifts into 3rd, revs are at about 5,200). However if I put it in tiptronic and change gears manually from 2nd to 3rd (before hitting max rev's in 2nd, so when changing into 3rd, revs are about 4,800) it will stumble for a split second at around 5,000rpm's. It wouldn't be a boost cut limit on the ECU that would be causing it would it?

 

I took it to the mechanic, he basically said because it could be a number of things he didn't want to know. I asked if he could check all the basics but basically got the cold shoulder... all I want is someone to do is a boost leak test, smoke test, check MAF, check O2 sensors etc. I don't have time to muck around with this,... time to change mechanics I think...

Edited February 25, 2014 by chimera

I'm still having issues with this. In 3rd or 4th gear, around 5000rpm's, stumbles (or feels more like a complete cut out) for a split second. Interestingly if I floor it in 'D'rive then it doesn't seem to do it (because when it shifts into 3rd, revs are at about 5,200). However if I put it in tiptronic and change gears manually from 2nd to 3rd (before hitting max rev's in 2nd, so when changing into 3rd, revs are about 4,800) it will stumble for a split second at around 5,000rpm's. It wouldn't be a boost cut limit on the ECU that would be causing it would it?

 

I took it to the mechanic, he basically said because it could be a number of things he didn't want to know. I asked if he could check all the basics but basically got the cold shoulder... all I want is someone to do is a boost leak test, smoke test, check MAF, check O2 sensors etc. I don't have time to muck around with this,... time to change mechanics I think...

 

Doesn't sound like a job for a mechanic. Sounds like it needs what you don't seem willing (able?) to provide... time, time to log properly.

 

It sounds like you have a tune issue, an issue that can only be diagnosed and corrected through logging and log review.

Doesn't sound like a job for a mechanic. Sounds like it needs what you don't seem willing (able?) to provide... time, time to log properly.

 

It sounds like you have a tune issue, an issue that can only be diagnosed and corrected through logging and log review.

 

I havent looked at any logs recently but when we did there is nothing that jumps out tune related. There is no boost error, no overboosts, no cels, no "freeze" in data, no knock, no feedback, no nothing during the event itself etc. The only thing I saw when pouring over logs *albeit a couple months back* was that during the issue the rpms would actually roll back a tad or stay in the 4500rpm range while everything else progressed through the pull....very strange indeed. I was honestly leaning tword an ignition cutout,collapsing intake or a trans issue. What's weird is him changing out the inlet tube helped temporarily which makes no sense.

 

Chimera - if the ecu was influencing the cutout in terms of a boost limit etc you would get a check engine light.that and the fact that the turbo is already starting to taper at 4500-5k so the boost is under control. Go ahead and email me and we can review a couple logs, maybe we can see something that was not jumping out on the last review.

 

Dave

Edited February 26, 2014 by cryo

I havent looked at any logs recently but when we did there is nothing that jumps out tune related. There is no boost error, no overboosts, no cels, no "freeze" in data, no knock, no feedback, no nothing during the event itself etc. The only thing I saw when pouring over logs *albeit a couple months back* was that during the issue the rpms would actually roll back a tad or stay in the 4500rpm range while everything else progressed through the pull....very strange indeed. I was honestly leaning tword an ignition cutout,collapsing intake or a trans issue. What's weird is him changing out the inlet tube helped temporarily which makes no sense.

 

Chimera - if the ecu was influencing the cutout in terms of a boost limit etc you would get a check engine light.that and the fact that the turbo is already starting to taper at 4500-5k so the boost is under control.

 

 

Dave

 

Compelling. It argues it may NOT be tune related.

 

While it has been a long time now, my '05 5EAT LGT also had a "weirdness" under similar conditions that I determined, after a long time, to be transmission related. It somehow had to do with how the tranny handled the torque converter lockup. All I know is, I learned to accept it and to stay in Drive if I didn't want the issue. Seems nothing I did eliminated it, but the more power I made the further along the torque curve it went, which became one of my metrics.

Chimera - if the ecu was influencing the cutout in terms of a boost limit etc you would get a check engine light.that and the fact that the turbo is already starting to taper at 4500-5k so the boost is under control. Go ahead and email me and we can review a couple logs, maybe we can see something that was not jumping out on the last review.

Thanks Dave much appreciated. I'll do several variations of logs tonight and see how I go. I loaned my tactrix cable to a mate for the past few months (you did his tune, as I referred him onto you) and have just got it back. I'll test with it in Drive and also manually changing in tiptronic

 

While it has been a long time now, my '05 5EAT LGT also had a "weirdness" under similar conditions that I determined, after a long time, to be transmission related. It somehow had to do with how the tranny handled the torque converter lockup. All I know is, I learned to accept it and to stay in Drive if I didn't want the issue. Seems nothing I did eliminated it, but the more power I made the further along the torque curve it went, which became one of my metrics.

Interesting, thanks for this. I'll do some more testing in D vs Tiptronic tonight.