Yes, NOx is created by high combustion temps, usually caused by carbon build up,(high mileage engines) BG 44k fuel additive works great to reduce carbon deposits.
On rigs where timing is not ajustable, motorvac service or 44k is the best solution.
Your O2 is working fine by those numbers, the swing from high to low is exactly what it should do.

Carbon increases temp by increasing compression ratio, like a diesel, they don't use spark to ignite the fuel, just heat created by very high compression ratios.

The best way to use 44k is to fill your gas tank normaly, add the 44k then drive (city type stop and go is best) till 1/2 a tank then top off again. This gets you 1.5 tanks with 44k in it. The worst is to add 44k then drive nothing but highway. 44k disperses the carbon when the engine is off and idling after getting to op temp.

Let us know the results and what you did.

NAPA and Carquest carry 44k $20 a can.


SD