Very bad misfire, P0302

Year/Make/Model: 2007 Mazdaspeed 6 (imported from U.S. -09)
Mileage: 103,000mi
Location: Finland, Northern europe
Concern: Cylinder 2 misfire. Rough idle, but doesn't seem to misfire every cycle. Normal idle RPM. Very rough stuttering under acceleration, and blinking engine light (P0302). Engine light stays on after activation unless deleted. Cruising with constant rpm produces the same condition as idle (random misfiring, not every cycle). Starts up normal. FRP around 1600.
DTC's: P0302, cylinder 2 misfire
Modifications: none
ECU/Tuning Software: original
Tuner: -
Is the concern intermittent?: started intermittent, now constant
Can you duplicate the concern?: yes
Recent Repairs: new plugs after first DTC (NGK 3787, .031"), new coil (plug and coil also swapped between 3&2), compression tested good and equal on all cylinders, injectors cleaned + tested (resistance and flow), new Corksport injector seals, maf checked, replaced camshaft position sensor. Currently at the shop where they will check the PCM and exhaust sensor(?) on 9/13.
Correction: -

Might have forgot something from the list. Sorry for not having the exact details on everything or the freeze frame data right now, I don't have access to the car until 9/13. Please, if you have any idea lmk. Thank you.

 

Regap the plugs to .026-0.028" , .031 is too big.

 

Sure, but the problem started before changing the plugs, and stayed on the same cylinder. The OEM plugs have worked just fine so far, might upgrade to .028 later, but I don't have them at my local part store. Got any other ideas?

 

you dont need to buy new plugs just regap the ones you have. and yea the idea is to eliminate this oversized gap which could be a major contributor to the misfire. its free and easy should take less than 30 minutes so why not do it.

 

is p0302 the only code?

 

I'll take a look at re-gapping the plugs when I regain access to the car, but OEM plugs with a .003" gap difference in a spec car causing a progressive misfire just doesn't sound right, considering that the misfire began before even touching the plugs.

Yeah, p0302 only code, never anything else, couldn't even get it to hop to another cylinder (tested switching the plugs, coil, and injector.)

 

its nearly 20% over spec and known to be an issue on these cars.

 

did u gap ur plugs mane

 

I just recently within the last month went through this cylinder two misfire. Moved coil pack to different cylinder and plug to a different cylinder. Still same cylinder misfire. Did compression check on cylinder. Was good. Next step. Look at your plug. The color will tell you what is going on. Mine was kind of dry and white. Not enough fuel. Removed fuel injectors. Cylinder two was caked. Couldn't even see the spray holes. Replaced fuel injectors, installed Corksport seals, cleaned valves while exposed. "Make sure valves are fully closed before cleaning to prevent debri down into cylinder." You can do this by turning the crank pulley by hand until you see them no longer move. Repeat for each set of valves. Reassemble with new intake gasket. Test operation. This took care of my cylinder two misfire. I know you did injector swap according to your post. So if not injectors, next could be cracked exhaust manifold on the cylinder. ( Again, plug coloration should point you to what is going on if your cylinder compression is within specs.)

 

Hey yall.
Little update on what's going on. Car is still at the shop (all sorts of weird things going on over there, mostly due to poor management) but their speed tech is taking a look at it again next week. They suspect something is wrong with the electronics.

What has been done since my last post:
-plugs were gapped + tested with brand new plugs with .028" at my request, no difference whatsoever
-everything on the exhaust side was checked and was okay
-plugs seemed fine after use, cyl1 maybe being slightly darker
-PCM/ECU will be taken a look at next week by their tech, connectors were already checked

I'll keep you guys posted on what happens next, hopefully this will help someone in the future.