High NOx emissions fix!

The guy I use for emissions testing here, told me today that he has always been able to fix and later pass high NOx (when there were no other problems) emissions, after they failed due to just high NOx emissions with one simple thing.

2 step fuel injector cleaner. The two step is one additive for the fuel tank, and the other additive is like Seafoam that goes into the vacuum lines, just like Seafoam instructions call for. I forget the brand name he uses, something like 2 step, but most of these products have the same goodies in them. He said he has them run those 2 additives and drive about 50 highway miles, and then reinspection passes them, when they previously failed for high NOX emissions.

So the obvious conclusion here is that carbon build up is part of the cause of high NOx emissions. And possibly some lean, partly clogging injectors. Or a mixture of both!

High NOX almost always means high combustion temperature. Usually it's because O2 is commanding lean but it can often be crap in the engine. One guy locally was getting it because his TPS was not registering WOT correctly...

His story definetely matches your "crap in the engine" version. 5-90 I think mentioned carbon build up once once or twice, in part from EGRs, being a common cause, but this guy sounded like he had cured hundreds of high NOx problems at his inspection station the last few years, with just "snake oil", LOL.

My guess is the fouled carbon deposits have a slow after burn effect in Low O2 areas, that causes localized high temps (activated carbon in other industries where I work comes to mind) that leads to increased NOx.

5-90 mentioned that my unusual head gasket failure (burned out between #4 and #5 cylinders, loss on compression, rough idle, but no coolant leaks, was caused by carbon deposits burning through the head gasket in that thin spot between the cylinder walls. He said the carbon deposits can get red hot, in localized deposits and lead to pinging, and other unpleasantries.