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Old 08-16-2021, 09:44 AM   #26
K3rm1tth3fr0g
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No offense to your diagnostic abilities, but I think this could be a situation where it could be beneficial to take the car to a shop with a fancy $1000+ scan tool to take a look at your setup to see what is wrong. You've tried most of the simple stuff.

My tuner was able to diagnose stumble issues on my WRX almost instantly. Experience helps when troubleshooting
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Old 08-16-2021, 03:41 PM   #27
DaveRosario
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Quote:
Originally Posted by K3rm1tth3fr0g View Post
No offense to your diagnostic abilities, but I think this could be a situation where it could be beneficial to take the car to a shop with a fancy $1000+ scan tool to take a look at your setup to see what is wrong. You've tried most of the simple stuff.

My tuner was able to diagnose stumble issues on my WRX almost instantly. Experience helps when troubleshooting
Not offended lol! That's a valid suggestion. I'm considering taking the car to an independent Subaru Specialist if I can't figure it out my self. I've been working on cars for over 15 years and have never ran in to something like this. But I'm new to Subaru. Like you said maybe some Experienced Subaru specialist might know better.
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Old 08-16-2021, 04:03 PM   #28
K3rm1tth3fr0g
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Originally Posted by DaveRosario View Post
Not offended lol! That's a valid suggestion. I'm considering taking the car to an independent Subaru Specialist if I can't figure it out my self. I've been working on cars for over 15 years and have never ran in to something like this. But I'm new to Subaru. Like you said maybe some Experienced Subaru specialist might know better.

You've done the simple stuff like boost leaking the car along with replacing the vital sensors like O2 and MAF, at this point I would personally hand the car off to someone who only works on Subarus (if there is a non-dealership Subaru specialist near you that is).

I would get the car tuned at the same time you get the repairs done (assuming you have a tuner and Subaru expert mechanic local to you). You may be getting this issue (not likely) from purely a non correctly calibrated ECU configuration.
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Old 08-16-2021, 04:33 PM   #29
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Originally Posted by K3rm1tth3fr0g View Post
You've done the simple stuff like boost leaking the car along with replacing the vital sensors like O2 and MAF, at this point I would personally hand the car off to someone who only works on Subarus (if there is a non-dealership Subaru specialist near you that is).

I would get the car tuned at the same time you get the repairs done (assuming you have a tuner and Subaru expert mechanic local to you). You may be getting this issue (not likely) from purely a non correctly calibrated ECU configuration.
The reason I started this thread was because I basically put the car back to stock and stock tune and the issue remains. I've tuned some civics and 350z/370z and even the old school 240z,260z,280z with triple carburetors and engine swaps including 2jz and LS engines (Sorry for all the bragging lol!).
I think I know what I'm doing and I'd like to learn more about Subarus. Probably if I handled the car to a Subaru specialist since the beginning it would of been fixed long time ago, but wouldn't had learned anything. I think that's the purpose of this forum, no?
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Old 08-16-2021, 04:33 PM   #30
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Quote:
Originally Posted by K3rm1tth3fr0g View Post
You've done the simple stuff like boost leaking the car along with replacing the vital sensors like O2 and MAF, at this point I would personally hand the car off to someone who only works on Subarus (if there is a non-dealership Subaru specialist near you that is).

I would get the car tuned at the same time you get the repairs done (assuming you have a tuner and Subaru expert mechanic local to you). You may be getting this issue (not likely) from purely a non correctly calibrated ECU configuration.
The reason I started this thread was because I basically put the car back to stock and stock tune and the issue remains. I've tuned some civics and 350z/370z and even the old school 240z,260z,280z with triple carburetors and engine swaps including 2jz and LS engines (Sorry for all the bragging lol!).
I think I know what I'm doing and I'd like to learn more about Subarus. Probably if I handled the car to a Subaru specialist since the beginning it would of been fixed long time ago, but wouldn't had learned anything. I think that's the purpose of this forum, no?
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Old 08-16-2021, 04:54 PM   #31
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Originally Posted by DaveRosario View Post
The reason I started this thread was because I basically put the car back to stock and stock tune and the issue remains. I've tuned some civics and 350z/370z and even the old school 240z,260z,280z with triple carburetors and engine swaps including 2jz and LS engines (Sorry for all the bragging lol!).
I think I know what I'm doing and I'd like to learn more about Subarus. Probably if I handled the car to a Subaru specialist since the beginning it would of been fixed long time ago, but wouldn't had learned anything. I think that's the purpose of this forum, no?
I am not against the concept of tuning one's own car, however you are running pretty far from a stock setup with the front mount, TGV deletes, radium fuel setup, 3 port EBCS, downpipe, injectors etc. A tuner/ Subaru shop would be able to rule out the tune as the cause of your issue - You've done everything simple I can think of mechanically.

Good luck.

Last edited by K3rm1tth3fr0g; 08-16-2021 at 05:02 PM.
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Old 08-16-2021, 06:11 PM   #32
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SO I do have a question, did the car ever run correctly? the biggest problem with these years is it takes alot for the misfire codes to come on. so its really hard to diagnose. I had one on my car that would come up at 4500 it was almost like a really really bad hesitation and the light still wouldn't come on. but if you have taken all the stuff off like the injectors and reflashed the oem tune and it still does it, it tells me somethings not right. it could very well be your flywheel but normally the street one is okay its the pro that usually has problems

Last edited by subaru_gc8; 08-16-2021 at 09:44 PM.
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Old 08-16-2021, 06:32 PM   #33
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Quote:
Originally Posted by K3rm1tth3fr0g View Post
I am not against the concept of tuning one's own car, however you are running pretty far from a stock setup with the front mount, TGV deletes, radium fuel setup, 3 port EBCS, downpipe, injectors etc. A tuner/ Subaru shop would be able to rule out the tune as the cause of your issue - You've done everything simple I can think of mechanically.

Good luck.
Thanks, Apologies if I sounded harsh.
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Old 08-18-2021, 01:44 PM   #34
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Quote:
Originally Posted by DaveRosario View Post
Ohh if your car is throwing codes it should be easier to figure out. Check the coils. Also log the roughness monitors and AFR, verify that your car is not running lean when the misfires happen. Did you do a compression and leakdown test? if not you should. If that's OK Then double check the timing belt is good and timing is all sync up.

I havent done a leakdown or compression test since it went to a local shop a year ago. I basically gave up bc I started working alot. I have monitored roughness before, not AFR and the shop I gave my logs to said everything checked out. They even hooked it up to a fancy machine and still they said it runs fine. I will look into what you mentioned thou! Thank you!
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Old 08-18-2021, 06:31 PM   #35
Router Rob
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I have been chasing the same problem for months. I've done much of the same testing and parts swapping as the OP. Do you guys think the fluidamper could have anything to do with it? It's heavier than the oem pulley. Could a heavy pulley cause similar problems to a lightweight pulley? I'm planning to swap mine out and see but it will be awhile before can get to it.

Robert
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Old 08-30-2021, 02:10 AM   #36
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Update:

I Installed the OEM Injectors back.. No improvement.

I noticed that I missed some open/close TGV tables and the car was switching to TGV closed tables while cruising. Once I fixed that and fine tuned the primary ignition timing tables, all the stumble/hesitation went away.

Now, some misfires still happen randomly at low RPMs, mostly when decelerating, shifting at low speed or parking.
These misfires can't be heard or felt as before. I only know because of the logs. The car runs way smoother now (as it should) while cruising.

No misfires while cruising or at WOT so far.


Some people say that all cars misfire here and there and is normal, some others say or report that their cars don't misfire at all.

What do you guys think?

I was thinking to open a thread and ask people with stock WRX/STI to log the roughness monitors and post their logs? to see what's the normal in these cars?
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Old 08-30-2021, 02:11 AM   #37
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Robert,

Please let us know if you change the fluidamper with the OE and if it makes any difference.

Thanks
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Old 08-30-2021, 07:06 PM   #38
Router Rob
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Quote:
Originally Posted by DaveRosario View Post
Robert,

Please let us know if you change the fluidamper with the OE and if it makes any difference.

Thanks
It's the next thing on my list. I'm going to do it soon. Hopefully in the next week or two depending on work and the weather.
Do you have a header and it so what kind?
Thanks
Robert
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Old 08-30-2021, 09:46 PM   #39
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It's the next thing on my list. I'm going to do it soon. Hopefully in the next week or two depending on work and the weather.
Do you have a header and it so what kind?
Thanks
Robert
Stock header and up pipe. Grimmspeed catted DP.
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Old 09-06-2021, 06:53 PM   #40
Router Rob
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Quote:
Originally Posted by DaveRosario View Post
Robert,

Please let us know if you change the fluidamper with the OE and if it makes any difference.

Thanks
Did it over the weekend. No change.
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Old 09-06-2021, 07:53 PM   #41
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2012 WRX with full built sti engine and having similar issue, no misfires but engine stumbles at around 2500-3000rpm, not always but enough to drive me nuts.
subscribed and watching, hope you guys figure it out.
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Old 09-07-2021, 02:43 AM   #42
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Quote:
Originally Posted by SuperPete View Post
2012 WRX with full built sti engine and having similar issue, no misfires but engine stumbles at around 2500-3000rpm, not always but enough to drive me nuts.
subscribed and watching, hope you guys figure it out.
It could be the typical STI stumble, which is caused by the stock fuel rails.
If you have TGVs delete, the ECU could be locking onto the wrong Ignition Timing table.
Vacuum leaks or any other issue where your AFR is affected.
Post a log
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Old 09-07-2021, 02:43 AM   #43
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Quote:
Originally Posted by SuperPete View Post
2012 WRX with full built sti engine and having similar issue, no misfires but engine stumbles at around 2500-3000rpm, not always but enough to drive me nuts.
subscribed and watching, hope you guys figure it out.
It could be the typical STI stumble, which is caused by the stock fuel rails.
If you have TGVs delete, the ECU could be locking onto the wrong Ignition Timing table.
Vacuum leaks or any other issue where your AFR is affected.
Post a log
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Old 09-08-2021, 10:21 PM   #44
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I have very good cobb certified tuner, who tuned my other subs and he knows what he is doing, I asked him to look in to the tav table, he did and confirmed that its all good there.
looking and comparing all the catalogs of the time of the hesitation I am starting to this its maybe has something to do with fueling, at the time of it happening I noticed pump usually switches its duty cycle from 33 to 66% or from 66 to 100, right before of the event, and I think maybe combination of throttle position, fuel jump and RPM's maybe that creates shock that changes pressure and creates this W in the log, like a shock waive.
my mods just FYI

2012 WRX with fully built forged EJ257, tav delete, air pump delete, evaporated delete,
FP green, process west TMIC, ID1300 DW350C, catless invidia and Q300, grimmspeed uppipe, 6 speed STI trans, grimmspeed air filter.
I am breaking in motor right now, 700 miles in to it.
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Old 09-17-2021, 12:44 PM   #45
SuperPete
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Quote:
Originally Posted by DaveRosario View Post
It could be the typical STI stumble, which is caused by the stock fuel rails.
If you have TGVs delete, the ECU could be locking onto the wrong Ignition Timing table.
Vacuum leaks or any other issue where your AFR is affected.
Post a log

SO I went back to the fuel pressure regulator, increased idling pressure from 44PSI to 50 and stumbling went away.
I was recording allot of logs and looking for patterns on when stumble happens, and I noticed that it always followed up on when pump shifts from 33 to 66% duty cycle, always at pump duty switch, so I figured that fuel has something to do with that, anyway, increasing pressure fixed it.
Now I am communicating that to my tuner to maybe keep that pressure and change pump duty cycle tables.
Anyway, good times, thank you all!
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Old 09-17-2021, 02:30 PM   #46
benflynn
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There is something going on, it shouldn’t stumble with dutycycle cycling, I’d verify the psi
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Old 09-17-2021, 02:54 PM   #47
SuperPete
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I did, I even replaced pressure gage itself.
Anyway, I think combination of the injectors pump and stock fuel lines was doing it, but once pump go 66 or 100% dutty, after 3K rom car is super smooth and pulls nice with very very healthy AFR, its right at that switch at the end of its 33% duty table, drains it out, anyway, changing duty cycle table will help
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Old 09-17-2021, 10:02 PM   #48
AliBenn
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Awesome!!!
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Old 09-18-2021, 10:34 AM   #49
SuperPete
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My tuner confirmed that this issue called fuel resonation, increasing fuel pressure helps, he also corrected fuel pump duty cycle to come on sooner.
Good to go, issue resolved, I hope this helps someone.
I will make quick video and post it on my youtube channel, explaining and letting it to a fix, I was searching for one, and I have not single video about subaru hesitation, coming up soon:

https://www.youtube.com/channel/UCwq..._z7mHuSB73ZaLA
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