Emissions Test... High "NOX" causes?

[EdgeKrusher4x4]

SO I Brought the Acura down for an emissions test and apparently since I've been gone to the military they started monitoring for NO2 or "NOX". I believe the Acura was failing on high NOX when they ended the test. I was thinking about what the possible causes for this would be... then a few weeks later I realized that the gas in the tank was very old. I am unsure of the condition of the Catalytic converter but the car runs great and has 91K on it. All 4 other gases are in spec and Check engine Light is not lit. Any ideas? Thanks!

Steve

 

[Will]

Well the EGR is designed to reduce the peak combustion temp by diluting the air/fuel mix with exhaust gas--that directly reduces NOx. The Catalytic converter converts CO, HC and NOx into CO2, N2 and H2O. One of those 2 things could be it. And old fuel could be at the root. No piece of the system is an island.

 

[MAKG]

You're in California. Did you pass the EGR functional test?

If timing is adjustible, you can get high NOx from advanced timing. But that should be on the test as well (along with idle speed).

One thing that won't be tested is a vacuum leak. That MIGHT trip a check engine light, but doesn't always.

 

[Ranger44]

Yup EGR or Cat

 

[MAKG]

It's an OBD-II vehicle. It has a cat monitor (downstream HEGO sensor). Unless the NOx failure was very slight, a weak cat will flip a code. If it WAS very slight, a replacement cat may fix it (for a while at least) even if the problem was elsewhere. It may or may not be cost effective; many 10+ year old cats aren't all that expensive.