New Motor- says it's misfiring but feels fine
 

Hello fellow RX8 nuts!

I have a 2004 RX8 GT with a 6MT.

As of two days ago, I finished swapping in a brand new short engine in my back yard, reusing most of the parts from my old engine. It started up fine on the first try, and runs beautifully. However, I get an intermittent flashing check engine light (misfiring) and an OBD code of P0302 (cylinder 2 misfire).

It doesn't do it all the time, and sometimes the code clears itself while driving, then comes back. I haven't been able to isolate the exact conditions that cause it to misfire, but it seems random. I'll be driving along, no CEL, then the CEL will start to flash and the code reader will give the above error, but nothing changes with the way it drives. No power loss, no losing rpms, no noises, it just keeps on exactly like it was doing before.

I figured it was the gnarly spark plugs that I reused from the last engine (I have a new set, but am going to break in the engine before replacing them), so I swapped the plugs between rotors, to no effect. Next on the list was the coils, so I switched those between rotors, again with no effect. I was hoping that the misfire would switch to rotor 1, and I could just replace the offending part, but at this point I don't know what could be causing this.

To the best of my ability I went through and made sure everything on the wiring harness was plugged in correctly and fully, but it seems like I would be getting other error codes too if a sensor wasn't plugged in or something.

During the swap I deleted the air injection system (black air pump next to the passenger strut tower and the silver pipe that connects to the exhaust manifold). I retained the bracket and connector, so it only gives a CEL for a minute or two on startup, then goes away when the car heats up and "shuts off" that system.

I also added the sohn oil adapter and am injecting valvoline TC-W3 two-stroke oil, and running Mobil1 synthetic 10W-30 engine oil. I replaced the oil injector nozzles and cleaned out the OMP lines during the swap too, so that system should be running fine. It is consuming oil out of the resevoir at roughly the right rate, but I have to guess on this as the bottle I am using isn't graduated.

If anyone thinks they know what might be causing this problem, please help! The car runs and drives great, doesn't feel like it's misfiring at all, but I want to make sure that I'm not destroying my engine so soon after doing all that work...

See the misfire link in my sig, still plenty of things to try. Good progress on the common stuff so far!

What is "your sig" I'm new to the formatting of forums. That probably is a very stupid question to you, but look at my post count...
Is it unusual to not be able to feel it misfiring?

Nevermind, it's in your reply. I feel so dumb. Reading it now, looks like what I need.

Yeah you generally will not feel the misfires. Try searching for the "brake stomp" method of resetting the sensor profiles. I bet it will go away after you do that :)

The brake stomping method solved my problem I think! I'll confirm in the morning on a cold start.
I did this the second time I started the motor, but I didn't know about the oil gauge sweeping, so I probably just did it incorrectly the first time. Or maybe it needed to be reset again?
Thanks for your help!

Thanks, but I have to give credit to Dannobre for that one, it was something I learned from him.

Question:
I assume that the battery has to be disconnected to pull the engine, am I right? If so, what does the 20-pedal-stomp reset do that the battery disconnect doesn't?

Disconnecting the battery doesn't reset the NVRAM.

Ah, nod. Good to know.