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Old 02-19-2018, 12:37 AM   #1
BarryDinpoon
Scooby Newbie
 
Member#: 482296
Join Date: Feb 2018
Location: Michigan
Vehicle:
2004 STi
Silver

Default Random -12 Feedback knock on acceleration

Hey guys,

I've been having an issue with my 2004 STI (157k, I think this is the original engine) where it just spikes with -12 feedback knock and I can't quite figure out what is causing it. I have a cobb stage 2 tune on it (I know, they're not the best but I bought it like this).

The car is mostly stock other than a processwest TMIC, Cobb BPV, and a custom 3" exhaust from the turbo. I'm running the stock intake.

Things that I know:
  • It typically happens in 3rd gear with moderate throttle application
  • It is usually around 4-5k RPM
  • AFRs are around 10-11 (I have an AEM Wideband gauge)
  • Oil Pressure is consistent
  • Spark plugs were just changed (OEM NGK)

When this happens, the car jerks and almost feels like it's cutting fuel. I usually get 93 from the same gas station but it has also happened with fuel from another gas station. It also usually backfires when it happens. I finally was able to get a datalog of it which can be viewed here. I've looked over this log and it's just not apparent what is causing it. Everything seems normal for the load range.

Any suggestions?
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Old 02-22-2018, 02:04 PM   #2
wgr73
Scooby Specialist
 
Member#: 232458
Join Date: Dec 2009
Chapter/Region: SWIC
Location: Las Cruces/El Paso
Vehicle:
2005 & 2008 STi
Cobb 20g & EFR 7670

Default

Does DAM drop as well, and does it only happen on acceleration or does it happen while cruising (under slight load) too? If yes, check compression.
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Old 02-22-2018, 10:03 PM   #3
BarryDinpoon
Scooby Newbie
 
Member#: 482296
Join Date: Feb 2018
Location: Michigan
Vehicle:
2004 STi
Silver

Default

Quote:
Originally Posted by wgr73 View Post
Does DAM drop as well, and does it only happen on acceleration or does it happen while cruising (under slight load) too? If yes, check compression.
I've taken more logs and I've noticed that DAM is starting to drop now. Almost every time it happens my car shows misfire codes for every cylinder.

It really only happens under acceleration and it doesn't matter what gear I'm in. I did a pull tonight that resulted in it changing DAM to 0 . Here's the log from tonight.
Here's another log from tonight that didn't change anything.

https://drive.google.com/open?id=19X...Pv-XCLdefq62Tm

I've added links to a few more logs. One of them didn't cause any misfires or DAM changes but the other one caused DAM to go to 0. I suppose it could be compression but I wouldn't think it would have low compression on all 4 cylinders at the same time... Stranger things have happened...

I should also note that it usually only happens once the car is up to operating temperature and if I do a pull around 100-130F it accelerates normally and builds boost fine.
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