Help me diagnosis my misfiring
 

Hey guys, how's it going.

I'm a bit frustrated at the moment, like the title says, my car has been misfiring recently. About a week ago I was driving and I decided to do a high rpm run and I was at about 6-7k rpm and my CEL started blinking (misfire) and I said well wtf... The next day I did an oil change switched to synthetic since my reman just finished the "break in" period. While I changed my oil, I checked my plugs and coils and thought it could be a loose boot from the wires. I disconnected all of them and reconnected them until I heard a snap from each one, also checked the boots on the coils. This was a couple of days ago.

Just now I went for a drive and I went up to about 7-7.2k rpm and once again I had another misfire. Went up high on the rpm again and confirmed the misfire again.

Related parts history:

Spark plugs and wires have about 8-9k miles. (I also just pulled them and cleaned them about 1k miles ago as well, they looked good.)
Coils have about 2k miles
Just got a reman from mazda, and it has about 2k miles.
My cobb ap is running the stock tune. (coolants temps are running fine from 180 to 200 f, AFR has been reading a steady 14.8 at idle and seems fine during higher rpm)
Battery is about to become a year old.
I'm running cat-less
Using idemitsu premix (half a ounce per gallon)
93 octane only.
Running an AEM cai.
Recently did a 20 stomp reset, battery reset, and cleaned my MAF sensor and ESS not too long ago.
Any other info I'm missing?

I honestly don't know what it could be... Before the misfires my car was driving beautifully, and was definitely not misfiring during high RPMs at all. I don't know what it could since my ignition system is practically new, and my engine too... I would really appreciate any feedback guys, this is pretty frustrating. I don't see any reason why my car would be misfiring, I really feel like it must be something stupid! :tear:

I already went through that.

Cleaned them!?? How?

OEM or some knock off?

Mmmmmm

Post data log and make sure you have all the logging options turned on. Ideally get a log that captures your misfire issue. What is "seems fine during higher rpm" to you?

Mmmm

Doesn't it smell great!


k

Perfect. Still could be a bad tank of gas. How many tanks have you gone through? Same gas station each time?

Did you check to make sure the Maf Screens where nice a straight?

You could have a bad Maf or Front O2 sensor or bad spark plugs/lead/coil.
Could be a failing fuel pump as well.

Post a Log and lets have a look at that and see if we can see anything else.

I posted it because there were several things in that list that you didn't mention that you did. Anything else that you have already covered?

Guys thanks, I really appreciate it!

wcs thankfully I won't be needed to post any of the additional info... I cleaned my MAF and ESS sensors last night just to get that over with. This morning I jacked up my car and removed all of my spark plugs, my rear trailing plug was cracked. The white ceramic piece had a crack that went down from top to bottom. I had a new T spark plug laying around so thankfully I was able to just replace it. I checked all of them and they all looked good, I reset my ECU and nvram and went for a drive it felt fine. Later tonight I'll be doing some WOT runs in the higher RPM range. I would imagine this was my problem as everything looks good.

How does the spark plug crack like that? I don't over tighten them at all, but they're not quite loose either.

It's very likely that's what happened. I usually use an extension after removing the wheel, all the plugs are easy to get to minus the rear rotor trailing plug it's a bit more angled. I noticed while removing it, it was also kind of stuck, hence the wear on the the sides of where the socket grabs onto. Anyway this time I made sure to tighten it all the way with my hand before using the socket. The safest way would be without the extension and tightening from under the car, rather than through the wheel.

Anyway, problem solved no more misfires. The car is back to running great, I did say I had a feeling it was something dumb...