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Discussion Starter #1 (Edited)
2016 sti
New Iag magnum closed deck short block w/14mm arp headstuds
Oem heads decked/ported/polished gsc s2 cams 272/272, beehive springs and titanium retainers, stock/oem valves not changed but valve lash (head work done at a mashine shop)
Iag Rails
Iag tgv deletes
Iag Comp aos
Iag phenolic spacers
Iag oil pickup/baffle/windage tray
-6an parallel ss braided lines
ID1300cc (not the new x2 injectors)
aeromotive adjustable fpr
Radium hanger w/walbro 450 hard wired 100% duty cycle
Cobb V3 Access port
Cobb flex fuel
Cobb fuel pressure sensor
Cobb Sf intake
Grim Speed 3 port ebc
HKS equal length headers
Grimspeed uppipe w/38mm tial ewg
Invidia catless downpipe
Fp Black turbo w/fp 84mm inlet
Aem wideband and gauge
Glowshift oil pressure gauge
Air pump delete
Cylinder 4 cooling mod
New NGK iridium plugs gap set to .029
Oem stock coil packs
gates timing belt kit w/water pump and new thermostat
12mm Subaru oil pump
removed banjo bolt screens
front mount prl intercooler
perrin motor mounts

Currently on a break in map
I have been monitoring cylinder roughness since i feel/hear misfire on idle and when holding rpm steady anywhere between idle and 3k rpm. Receive P0300 and P0000 (while vehicle is stationary 0 speed) (idle set to 950rpm)
Idle: cyl roughness count is 1-2 on cyl 4 every now and then (smooth idle)
Hold rpm 1200rpm; cyl roughness cyl1-5 cyl2-5 cyl3-1 cyl4-11
Hold rpm 1500rpm; cyl roughness cyl1-61 cyl2-3 cyl3-1 cyl4-18
Hold rpm 1700rpm; cyl roughness cyl1-9 cyl2-7 cyl3-1 cyl4-22

while driving/cruising misfire counts are rare and if i do get any its a count of 1 on cylinder 1 and 4
I have spent 3 weeks diagnosing this issue with my tuner
I have moved coil packs/plugs/injectors around with misfires not changing (even reinstalled my old 1050x injectors that I know were working flawlessly and issue still there)
I have monitored avcs and its +- 1 left to right for both intake/exhaust
no fuel leaks, fuel base pressure set to 43.5, cleaned maf, map, crank sensor, both cam sensors, cleaned/tested oil control valves, I even added 3 grounds, triple checked timing marks, I have spent the last 3 weeks reading and trying what ive seen in forums with no luck.
I ran a compression test even though this build only has 200miles and ring are not seated yet (hot test)
Cylinder 1- 94
Cylinder 2- 94
Cylinder 3- 97
Cylinder 4- 97
I also performed a pressurized boost leak test (10 psi) and smoke test and passed. (told the shop about these compression results and said that's normal.

Today I had a shop in Colorado Springs run Diagnostics and after 3+ hours they didn't find anything. (shop performed smoke test and passed) I will be dyno tuning with this shop, they said they would need a couple day to fully diagnose the issue but at $140/hour that's gonna get expensive real quick.

I am sure there is something I have done that I missed to mention here, I am out of ideas and don't know what else to do please help.
 

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My guess is that you are misfiring because your compression is so low. Mid 90s, I'm i reading that correctly? If the fuel/air mix cannot be compressed properly it will lead to uneven burn/ inadequate combustion. That most certainly would result in a misfire. Just a hunch though. Good luck man.
 

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Discussion Starter #3
If that were the case then wouldn't every built motor with new short block/internals misfire the entire break in period untill the rings are seated, I would say otherwise if the motor already had a couple thousand miles but not new. Thanks for the help tho.
 

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I have a new IAG stg 4 with new everything in breakin and have almost the EXACT same issue As OP.

My misfires are on bank 2 only, with no load. Driving I see hardly anything of concern on roughness counts. I am running IW1700s and my tuner insists we’re fine, that the injectors are the culprit. My shop thought it was a bad tank of gas because it just started happening with no changes, but not sure about that since I’ve refilled with 93 again.

Like yourself, cant leave this alone. Perhaps we can share info on mutual troubleshooting!
 

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Discussion Starter #5
Originally I was running my fuel feed parallel and returns T into the fuel pressure regulator, I have split them up and now running a return individually to a port on the FPR, this seems to have helped a bit, idk how your fuel system is set up, I'm currently waiting on a in line radium fuel damper to run in the feed and see if that helps. My tuner thinks it might be harmonic pulses in my fuel system. I also have my own break in map I made to try some things out; decided to force open loop in the tune and commanded 13.5 afr in the trouble rpms and roughness counts are now only on Cyl 1 & 2, I'm thinking my tuner may be right and might have to do with fuel. My previous setup before this build I was using cobbs fpr which has a damper and no issues and should have the radium damper installed soon so I'll post an update.
 

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Originally I was running my fuel feed parallel and returns T into the fuel pressure regulator, I have split them up and now running a return individually to a port on the FPR, this seems to have helped a bit, idk how your fuel system is set up, I'm currently waiting on a in line radium fuel damper to run in the feed and see if that helps. My tuner thinks it might be harmonic pulses in my fuel system. I also have my own break in map I made to try some things out; decided to force open loop in the tune and commanded 13.5 afr in the trouble rpms and roughness counts are now only on Cyl 1 & 2, I'm thinking my tuner may be right and might have to do with fuel. My previous setup before this build I was using cobbs fpr which has a damper and no issues and should have the radium damper installed soon so I'll post an update.
On my setup both bank’s line go direct to an aermotive FRP without a T. Seems similar to your.
 

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Discussion Starter #7
Well after installing the damper I just wanted to report back, unfortunately my misfires are still present, hopefully someone else will chime in and help us out.
 
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