pilleway

Good morning all! I do have a C2500 having problems to comply with NOx in the in use verification, the two Cats have being replaced as well as the O2 sensors, I had Cat low efficiency as well as O2 sensors not switching codes, I have seen that after O2 sensors were replaced it had P171 and P174 (system too lean in bnk1 and bnk2). (I'm thinking to clean the inyectors, fuel pressures is OK)
Do any of you know what is causing the engine to generate to much NOx's? and what can be done to fix it? In all days with the carburetor engines you were able to adjust timing and fuel and be able to fix, but know with the new electronics there is no way you can adjust fuel and spark.
The vehicle has 140k+ Mi., no oil consumption, it works OK.
Any comment/help/recomendation will be grately appreciated.

Have a nice day.

EinST

Take care of P171 and P174 and NOx should take care of itself. A chemical reduction (reverse of oxidation) of NOx into nitrogen molecules takes place inside the catalytic converter. In order for that to happen, something has to take up the oxygen atoms. That something is incomplete combustion products (hydrocarbons, CO, and even hydrogen). When the engine is running lean, there's too much oxygen in the combustion chamber and in the exhaust and thus the condition is ripe for too much NOx formation and too little reduction reaction.

pilleway

Einst, thanks for your information, I will look in to the 171 and 174 codes, I do not know were to strart, a tune up was done recently and I think that it might have a none control air intake and/or a partialy plug injectors, also I think I will check for fuel pressure.

Thanks for your coments.

EinST

You're quite welcome. For some reason I'm drawing a blank on what you mean by "none control air intake." Anyway, I don't know the history of this vehicle but it's probably not likely that all the fuel injectors would get plugged up at the same time. I concur on the fuel pressure check but don't forget that there could be an air leak or the MAF sensor may be underreporting.

pilleway

EinST, thans again!
What I mean by none air control, is an air leak between the Throtle body and the cylinders, the engine might have air entering due to a bad gasket or a broken hose, you name it.

I will look in to the engine soon, if I do find something I will report it.

Have a nice weekend.