i just got catted helix down pipe and tuned to ca91 stg 2 with cobb. every day i get a loud backfire and a CEL. every morning the CEL is gone. today i brought bu cobb with me and when the CEL went on i immediatly checked it. CEL P0301 (cylinder 1 missfire) what could cause this. ive looked on the net but cant find a cause. one person reported it due to a light weight crank pully - i have one too. another reported it due to rev limiting (over rev). i just want some imput please. im getting a pro tume from Ed at EQ tuning next month maybe that will fix it.

please help thanks

 

i had the same problem before i got tuned and i checked it out at nasioc and some guys did say it was because of a lightened pulley. some guys also said that changing the spark plugs got rid of it. when i was having the problem i was going to change my spark plugs, but after i got tuned it went away.

 

Cylinder one missfire detected.
When was the last time you changed your spark plugs?
You should always keep up on your 30K mile services.
Before you get your Protune change all your spark plugs,
clean your MAF sensor.
This will probably resolve your problem.
Good Luck.

 

well i only have 9000mi on my car, its 5 mo old. can the spark plugs be bad already? also WRX409 said "clean maf sensor" i heard this from a friend over the weekend, he said to toss the perin drop in filter - because its an oil one and the oil will mess up the MAF.

 

Oiled (even new from factory) filters WILL cause problems with the MAF cars (K&N, Green, Perrin, et. al.). Go with HKS, STI or AEM or any other DRY filter. If you don't believe me I have a K&N I'll sell you... cheap.

 

Wow...some serious misinfo....... bad mass airflow meters will very very rarely cause just one cylinder to misfire. Actually they will usually cause a mass air flow code to show up. If you have a cylinder one misfire, If you have access to subarus diagnostic system it will tell you if its primary or secondary. Primary equals no signal to plug. Check your coil packs etc. Secondary means check that plug. If you only have 9k miles, then go to your dealer. Plugs are covered for the first 12.5k of the vehicle. But if you really would like to know what it is.....your mods are messing with your car(to rich, to lean). Get it tuned right with new plugs, maybe a step colder and call it a day. Ofcourse all other problems are caused by oiled filters. My spt caused me to have a flat tire the other day........

 

well i took off the bov and the problem went away... what was it doing to cause a miss fire could it have been runing too rich to ignight or something?

 

Perzactly. The computer expects a rush of air into the intake from the factory bov that is not atmospheric, so it sends a burst of fuel. When you put an aftermarket that vents to atmosphere or does not completely vent to the intake, then the computer still sends that burst of fuel. Which might cause a rich enough environment to keep one of the cylinders from firing. It also causes that cool flame effect out of the exhaust and the not so cool bogging down between shifts. My hks never threw a code but definitely did the last two. Track days sucked because of the fluffiness between shifts so I sold it to one of my mechanics with an rb25 in his 240.........But it could still be that devious air filter of doom thing

 

I've had a misfire code for every cylinder.
It started when I went with bigger injectors and from what I'm told it's very common when running higher than stock flowing injectors.