Good knowlege on emmissions problems needed...

[JonIsConfused07]

I just got a '95 Nissan Altima SE. The car is in great shape and drives very nicely, however, i'm getting screwed on emissions and my car won't pass inspection! this is the second time it's happened already and i need to get it fixed! the car will not pass because there's too much NOx in the emissions. we tried to repair the EGR valve and instead of fixing the problem, the readings we're higher this time around. if anyone is familiar with how to reduce the NOx (the limit is at 2.50 points, i'm at 6.85) then please respond with you're theory.

[JustSayGo]

My theory is that there is still something wrong with the EGR system. High NOx is from combustion temperatures being too hot when the fuel is burned. The EGR uses a small amount of exhaust metered into the combustion chamber to cool off the fire similar to the way that a fire extinguisher puts out a flame. Both the exhaust gases and what ever is used in the particular fire extinguisher don't have oxygen. Does the engine run rough at idle if you put vacuum to the EGR valve? Either the exhaust to the EGR valve is plugged or there is no vacuum going to the EGR valve. The repair manual says that there is a slit machined into the throttle body that can get blocked and stop the vacuum signal that is used to open the EGR valve. Have you checked the EGR valve diaphram for a vacuum leak? Have you checked the vacuum hose from the EGR valve to the canister to see if they hold vacuum and that the canister solenoid valve doesn't leak vacuum and opens to let vacuum through?