About 2 weeks ago, I started my 2011 Infinity G37x to a rough idle. Once I turned into a main road and began to really accelerate, my CEL began flashing, and it was very clear the engine was running more harsh than usual. After immediately turning around and running a scan, I found cylinder 5 was repeatedly misfiring (P0305.) Since then, I've replaced spark plugs (properly gapped), replaced the drivers-side valve cover spark plug gaskets (as one was leaking), checked ohms on and have swapped ignition coil packs, checked battery voltage to 12.1V, checked for vacuum leaks, and have tested the wiring to at least cylinder 5, where nothing was outstanding as wrong. Despite this, I've been getting multiple cylinder misfires ever since (P0300.) Only two other things stood out of the water to me which was a code P0106 (MAP/sensor) getting thrown only one time and not since I've cleared it, along with bank 1 seeming to run extremely lean with fuel trim fluctuating much more than the other bank as well. While bank 2 pretty steadily cuts fuel at idle around -4 or -5, bank one would trend around +25 and often drop to +5 then quickly move back to +20s. I've read that I should check the fuel system, MAP sensor, and O2 sensors although I'm really unsure of where to go from this point. Thank you in advance for any help

 

Did you ever get to the bottom of the problem? I have a car that I picked up cheap that I love, but I have a similar issue that presented similar in cylinder 4 for me. Similar fuel trim behaviors also. My P0304 was the only code thrown at the time. I got my ride home and the left cat was glowing red. Pretty sure it was dumping fuel into the exhaust and just flame throwing that cat. Surprisingly, the Air/fuel and O2 sensors seem to be acting pretty normal so far from what I can tell; A/F fluctuates values often and the O2 is pretty steady around a particular value. Unless I'm wrong about that. I'm pretty new to this. I replaced plugs that were beyond really bad, coil packs. The idle actually got worse. Still just the one code; P0304. I have a feeling I have a bad injector but I'm new to these cars and am not sure how likely that is at 100+k. Anything is possible considering the condition I bought it in. I think that I have multiple issues at once so I'm just wondering what went on in your case, or if you got to the bottom of it?

 

Responding to: Gx•a=infinity;4299245
I was able to finally source the problem down to a short-circuit within my engine control module. The short caused miscommunication between the engine and ECM, allowing a constant voltage to flow when it wasn't supposed to be. Was able to check this by connecting a multimeter to the spark plug wires leading to the coil pack (2 of the 3 connectors should be receiving voltage with the vehicle on a running.) The issue can be seen when there is still a voltage reading after the car is shut off. A properly functioning ECM will cut voltage to the coil packs, whereas if there's an unknown short, electricity will continue to flow (as it was in my case, with the wire to cylinder 5). This problem is obscure to say the least, and I wouldn't put my money on that causing your misfire, but its definitely worth a check if you've expended most other options like I did. If I had to guess exactly what'd be causing your misfire on the spot, I'd say a clogged catalytic converter on your left side as they should never really get glowing hot. Especially considering that only one CAT was running that hot and there's a misfire on the same bank, it's possible that too much backpressure is being created by a clogged CAT itself. Again, all of my knowledge is very intro-level and everything I just said should be taken with a grain of salt, just hoping I at least steer you in the right direction 🙏🏼