Hey everyone, I’m looking for some help diagnosing a persistent misfire issue on my 2011 G37x Sedan with just over 108k miles.



It started two days ago when I noticed the car idling very roughly right after startup. I scanned it with an OBD2 reader and got a P0301 code—misfire on cylinder 1.



Naturally, I started with the basics:

• Replaced all the spark plugs with new ones.
• Swapped coil packs from bank to bank to see if the misfire would follow.

While doing that, I noticed a bit of oil in the cylinder 1 spark plug well, so I assumed it was the valve cover gasket. I replaced it the same day, used RTV where needed, and waited 24 hours before starting the car again.



Next day: still rough idle, and now I’m getting misfires on cylinders 1 and 3 (P0301 and P0303).

Did I mess something up? I checked again—no oil in the wells anymore, so the gasket job seems solid.



I then suspected bad fuel, since I had just filled up the night before the issue started. Maybe I accidentally put in something lower than 91 octane? I tried an octane booster, but it made no difference.



Next step: I swapped the fuel injectors between banks. Still no change—same misfire codes on cylinders 1 and 3.



Then I thought it could be the catalytic converters, since I’ve had a code for them in the past (I always assumed it was just a sensor). I removed the cats and inspected them—they looked fine.



Head gasket? Doesn’t seem likely:

• No smoke from the exhaust.
• Coolant looks clean.

Piston rings? Also unlikely, right? Wouldn’t that also cause smoke?



I even did a compression test on all cylinders, and the results were perfect.



At this point, the only thing I haven’t tried is replacing the MAF sensors. They seem fine, but just to be sure I’m going to AutoZone today to pick up new ones.



Honestly, I’m at a complete standstill. If the new MAF sensors don’t fix it, I’m probably going to have it towed to Nissan for diagnosis.



Any ideas or suggestions? I’d really appreciate the help.