[LkDuggan1311]

Hey all,

I have searched and searched online and can’t seem to figure out what is going on. I have a 2005 STI with a newly built motor (1,925 miles at the time of this post)

the block is an IAG stage 2 with the heads having been rebuilt and what not. It’s running 24 psi of boost on an FP black turbo. 1000cc ID injectors and upgraded fuel pump along with cobbs flex fuel setup and accessport. Once the motor was broken in 500-1,200 miles I went to the local dyno and had it tuned by a reputable tuner. The car was making 430whp on e85. So everything was all fine and dandy. Then one day (probably about 2-3 weeks after the tune) I throw a CEL. I check and it’s a misfire code for cylinder 2. Well I clear the code and it’s fine, no other CEL for a couple of days and then it starts again and this time it’s a different cylinder, I clear it and ride around to see and it comes back and it’s another cylinder.. needless to say I get in contact with my tuner who currently is having me send him a datalog. But utilizing the Cobbs misfire readings, the car is throwing misfires in cylinders 1-4 primarily 2 and 3 when idling. Like sometimes on start up cylinder 3 can get as high as 80 misfires as soon as it cranks but then evens out. Currently typing this after driving it to my mother in laws the car is at idle but threw 35 misfires in cylinder 2 once I pulled back into the driveway and having it idle. What stumps me is under load while driving it’ll have a misfire here and there in any of the 4 cylinders but typically is 0. It’s never a constant thing either. One day it’s one cylinder throwing what I read as an insane amount of misfires and then others it’s a completely different one. I have already changed to new spark plugs and new coil packs. Still reaches 24 psi and seems to run great once I am driving.
Does anyone have any idea what it could be while I’m waiting for my tuner to get back with me?

feel free to ask for further information and sorry if the lengthy kinda confusing post.

thanks I’m advance

 

[LkDuggan1311]

This is currently while idling and the misfires in cylinder 2 I was talking about.

 

[mheyman]

Issue? Who knows . . . I'd guess timing or ACVS?

Lot of parts not mentioned, but they seem to be mismatched.
* 1000cc injectors tor a FP Black on E? Were they the limitation at 430?

 

[LkDuggan1311]

Issue? Who knows . . . I'd guess timing or ACVS?

Lot of parts not mentioned, but they seem to be mismatched.
* 1000cc injectors tor a FP Black on E? Were they the limitation at 430?

Got two brand brand new AVCS complete sprockets when the motor was built. Along with OCVs. I got the 1000cc injectors just because that’s what the tuner recommended to me but I believe those are what is keeping me at going to much higher than 430whp.

I have a data log I can post if anyone cares to look.

 

[LkDuggan1311]

Can anyone explain why if I unplug the front O2 sensor the Accessport shows no misfires anymore? Can’t tell if this is fixing the issue or just Cobb somehow utilizes this sensor with others to measure misfires.
This O2 sensor was replaced by an OEM before the issues/tuning so I’m unsure why this would be the problem 🤔

 

[AustinSedz]

I assume your coils and spark are new if you did a new block?
Idk 100% about Subarus but my understanding is that misfires are detected by the crank position sensor.
My first move would be to check that sensor.
Not sure why the o2 would effect the misfiring but maybe if the car loses o2 feedback it pulls timing so the 'chance' of it happening is far lower.
I'm no tech, so I'll let the experts chime in, but since it wasn't an issue at first, my guess is something worked itself loose.

 

[LkDuggan1311]

I assume your coils and spark are new if you did a new block?
Idk 100% about Subarus but my understanding is that misfires are detected by the crank position sensor.
My first move would be to check that sensor.
Not sure why the o2 would effect the misfiring but maybe if the car loses o2 feedback it pulls timing so the 'chance' of it happening is far lower.
I'm no tech, so I'll let the experts chime in, but since it wasn't an issue at first, my guess is something worked itself loose.

yes I got new coils and plugs with the build. Yeah I wasn’t sure about the o2 sensor that’s why I asked. Not sure how it would detect being it’s not able to read each cylinder.
Still waiting on my tuner to get back but it’s been weeks. So I’m trying to not get frustrated but then again I’m having to drive the car due to it being my only daily.