CEL P0301 came up today

[Sportsguy83]

So I got the CEL flashing twice today, pulled the code and its P0301, misfire on cylinder #1.

After getting to work, I let the car idle for a good 5-7 minutes to see if I had a rough CEL but nothing. Its smooth as butter.

I was running a new map that was running RICH. I will go back to the previous map to test if it happens with the old map too.

Not trying to cause panic or mass hysteria, just sharing. I will update later on if it is a coil pack, bad DI seals, just a random misfire, etc.

UPDATE: So I flashed back to previous tune, and Hit the car HARD, no codes. No misfires, no anything. I'm inclined right now to say it was the extremely rich condition.

Final Update, #2

I wanted to update I resolved my issues with the CEL P0301.

The closed loop/open loop transition in my car while running E85 was EXTREMELY rich, (AFR went down to 9) and this caused a misfire condition.

I asked my tuner to lean out the transition and now it only goes down to about 10.2, no more CEL.

This happened a few months ago but randomly saw this thread and wanted to let everyone know that may be your cause.

[infinite012]

It's the engine!

Get a new one.

[FR-S Matt]

Looks like you have to go back to N/A, David!

[aagun]

check DI seals
@@@

[Sportsguy83]

Originally Posted by aagun

check DI seals
@@@

Yeah, it might come to that eventually, but I will rule out other possibilities in the meantime. Idle should not be rock solid and with no popping noises if it was the DI seals.

[aagun]

that things happened with me ..
my dealer ship change one of my DI injector , they tolled me the nozzle needle is Stuck and the injector is damaged , maybe the fuel and overheated engine with hot weather coz that damaged
it popping @ 2500 - 5000 rpm with misfiring. but without CELs!

[Sportsguy83]

Originally Posted by aagun

that things happened with me ..
my dealer ship change one of my DI injector , they tolled me the nozzle needle is Stuck and the injector is damaged , maybe the fuel and overheated engine with hot weather coz that damaged
it popping @ 2500 - 5000 rpm with misfiring. but without CELs!

Thanks a lot for sharing the information!

[Sportsguy83]

So I flashed back to previous tune, and Hit the car HARD, no codes. No misfires, no anything. I'm inclined right now to say it was the extremely rich condition.

[Carwhisperer]

Got p0351 about a week ago. 1st cyl malfunctioning on johns latest tune. I heard misfiring this morning. Car runs perfect on the stock map.

[Apoc]

Another cause may be the LW Pulley. I had a P0304 a few weeks ago while I crusing with the RPMs about 6k and I think the accel/decell switching back and forth rapidly may have triggered a false misfire detect. This had been an issue on earlier Subaru LWPs from Perrin and they made the FA20 pulley a bit heavier to help prevent this. The CEL flashed for about 15 secs and stopped by the time I pulled over. I saw no other symptoms other than the CEL. No rough idle, no stumbling, no power loss, just smooth rev all through the RPM range. Had I not seen the CEL for the few secs it did flash I would have never know it happened unless the code history was pulled. I have been waiting for it to re-occur but hasn't and I have continued to drive hard. If it ever pops up again on the same cylinder I will take it in to get checked.

[Sportsguy83]

Originally Posted by Apoc

Another cause may be the LW Pulley. I had a P0304 a few weeks ago while I crusing with the RPMs about 6k and I think the accel/decell switching back and forth rapidly may have triggered a false misfire detect. This had been an issue on earlier Subaru LWPs from Perrin and they made the FA20 pulley a bit heavier to help prevent this. The CEL flashed for about 15 secs and stopped by the time I pulled over. I saw no other symptoms other than the CEL. No rough idle, no stumbling, no power loss, just smooth rev all through the RPM range. Had I not seen the CEL for the few secs it did flash I would have never know it happened unless the code history was pulled.

I have had it come again twice in the last few days, both times on deceleration and maybe 4K RPMs. No rough idle or any of the other symptoms. Wondering if its LWP and LW FW. Might pul the pulley out if it keeps doing it.

[Carwhisperer]

I also have had 1st cyl malfunction/misfire. I have a perrin LW pulley as well. After the toyota tech did some diagnostics and found nothing wrong it hasnt popped up since. I bet he reflashed though.

[ImperiousRex]

I get the P0302 CELs occasionally on track (usually when I'm in a spinout) and I'm also running the Perrin LWP. I know at least one other guy on track that experiences the CEL with the same LWP.

It's usually a soft code and clears itself though. I haven't had any other issues with the engine.

[Sportsguy83]

Originally Posted by Carwhisperer

I also have had 1st cyl malfunction/misfire. I have a perrin LW pulley as well. After the toyota tech did some diagnostics and found nothing wrong it hasnt popped up since. I bet he reflashed though.

I'm a little concerned (not too much) as I don't have any other bad symptoms.


The only thing I can think of is that I got it once and ONLY once on an extremely rich tune (as soon as I flashed a different file it went away), and now I am running E85, so again it is dumping a good amount of fuel into the cylinder.


I'll keep this updated.