ok i checked the egr valve and all of the hoses and tubes. they were all good. my cat is still the origional one with 126000miles on it so that would be my next guess. is there any thing else that could also cause this?bahearn said:The catalytic converter also affects NOx emissions. After you've verified proper operation of the EGR system (don't forget that tiny pipe that easily clogs with carbon), and if you still fail the test, replace the cat.
Only if you fail the HC or CO portion of the test. NOx is affected by EGR, cat or timing. You could try retarding timing a couple of degrees to cool combustion temps a smidge.BrookShadowRC said:What about O2 sensor? I seem to remember the Nissan dealer saying that this might also need replacing if emissions continue to be high? Any thoughts?
Did you actually test the EGR with a vacuum pump and vacuum gauge like Lew posted? I say this because I cleaned my EGR since I was getting pre-ignition/pinging at very light throttle. Everything I read said it was caused by the EGR not working properly. The whole idea is combustion temperatures get too high, NOx increases. Also, advancing the timing could contribute. I even changed my thermostat to the OEM 170 degree temperature, from the 180 degree one I replaced a while back. So, there is a domino effect. Things that increase combustion temperatures increase NOx.ok i checked the egr valve and all of the hoses and tubes. they were all good.
I am curious about the tiny pipe that easily clogs. It's specific location would be nice to know.After you've verified proper operation of the EGR system (don't forget that tiny pipe that easily clogs with carbon)