P0303 - Engine Struggling and Rumbling
 

Hi! Need some help with a returning P0303.

Some historical events -

My 13 BRZ (2015 FA20 swapped) threw a P0303 last month and I took action by replacing the spark plugs and the coil. Both plugs and the coil are OEM from a Subaru parts center. Did the job and reset the code. Everything was great, I even got an MPG improvement. Drove 300 miles and still great.



Today -

Went to Laguna Seca to do a track day and my first two sessions went well. During my third session, the car started to have a distinct rumbling exhaust note, power loss, and blinking CEL. Pulled into the paddock, turned off the car, and checked for the code. Code was P0303. I decided to pack up and leave. I cleared the code before leaving.

On the way back home, the symptoms came back and it struggling. At times the issues were intermittent, it was struggling/bogging and then things feel fine for a very short time, within seconds. Then goes back to the struggling, bogging, power loss, blinking CEL, and rumbling exhaust note.


I'm starting to think that cylinder 3's injector is bad. Not totally sure though and I don't want to start chasing a problem blindly. I did some data logging on my OFT v2, but I have no clue how to read it.

Here is my data log:

https://drive.google.com/file/d/1jPV...ew?usp=sharing

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Relevant aftermarket parts for the P0303.

JDL Catted UEL
Stage 2 OFT OTS Tune
Tanabe Over Pipe
Tanabe Front Pipe
GReddy SP Elite Cat Back

Would love to get some insight from my fellow 86 owners.

https://datazap.me/u/kev0/hachigoku?...ta=3-4-6-10-11

In the future, upload your .csv files onto Datazap for better readibility

Oh this awesome, thank you!

I'd suggest you replace/swap the #3 coil (again). Maybe your track adventure did it in - :iono:

Resolved it. Coil died. Swapped it and I'm back on. I think I'm going to get some upgraded coils for the next track day.

Do you have the new style coils or old style? I keep killing the front passenger side one on track at the very tippy top of 4th I will throw the P0301 code. Hood vents could help as its heat that's kills the coils. Also I would take the part back to the dealer and get a new one. Might have been defective.

Swap to the upgraded engine harness and 2015+ coils....you'll never have the issue again.

Yea I know :)

I have the new style. The Racer's Line moved over the harness from the 2015 engine into my 2013.

Sounds like something in the harness is shorting the coils...possibly a loose pin in once of the connectors...or a cut in a wire.

Not sure, but I think failure is caused by the coil itself. Its the cheapo Autozone coil I used. Which is a Duralast brand. Will be buying OEM and seeing if that fails on the next HPDE day.

Oh yeah, I wouldn't trust an aftermarket