This is a log I did on first start up and warm-up after all parts replacement. Does it look normal?

 

Not at all...
Your AFR should be a stable ~14.7 at a warm idle.
The log shows the AFR dropping to 9.9 (which so rich, misfires can happen) for about 3.4 seconds, then it slowly rises from 9.9 to 12.9 over the next 5 seconds.
Then it stays in the 12s over the next 22 seconds.

The short term fuel trims correlate to the AFR, meaning the ECU is trying to cut fuel, but after -25% fuel correction, it gives up, resets to 100% and the AFR goes back to ~9.9



Your MAF flow (g/s) look to be in the typical range for a warm idle of about 4-5 g/s
(to estimate g/s at idle, the displacement is the about the g/s... for a 3.7 v6, it should be around 3.7 g/s)

Sooooo, the engine is running rich and the fuel trims can't be lowered enough (75% in EcuTek or -25% for most OBD apps) to get the AFR to 14.7 / lambda 1.0, the ECU gives up, and then tries again and again.
Off the top of my head, I can think of two possible sources of additional fuel being added.

(1) Leaking fuel injector
Yes, I know you have replaced them. To verify, purchase a" Nissan Fuel Tap" (I've used this one... https://cj-motorsports.com/products/fuel-tap-npt-2-bolt) and a cheap 100 PSI gauge.
I've used a $10 from a pool pump.
Start the car and verify the fuel pressure is about close to 52 PSI. Then turn off the car and wait 30 minutes. If the fuel pressure is below 30 PSI, you may have a leaking injector.

(2) Problem in the EVAP system.
Additional fuel / vapours from the charcoal / evap canister / system can provide additional fuel.
To test, disconnect the evap tube at the intake manifold.

That's all I got

 

Did anyone ever solve this issue or has everyone pretty much given up? I’ve also been fighting a similar acting P0300 for years and I’m at a loss. Feel free to view my post at the link below and maybe someone can point me in the right direction. Thanks!

https://www.myg37.com/forums/g37-sed...st#post4342414