Need help too much NOx

[SpdElemts]

I went to a the smog shop yesterday and the guy was nice enough to give me a free pre test. I put my friends stock exhaust and cat from his car that passed to put on my car and it did get better then the last time i tested but not enough to pass. (15mph=1025 25mph=1045) The guy told me to hold the egr valve all the way open as he ran the car and the NOx jumped from 1025 to 400.....i tested the egr valve, transducer, and solinoid as instructed in the FSM and all is working. Also as i rev the engine the egr valve moves up and down. Anybody know what else can be the problem?

Thanks, jeff

[DAEDALUS]

Your combustion temps are too high. High temps cause NOx. Opening the EGR displaces O2 in the chamber, so less fuel burns (the HC reading should have increased when you did that). Why the temps are too high you'll have to figure out. Your spark timing could be retarded, or cooling system's not doing its job. If the car doesn't seem to be running to hot otherwise, check your timing first.

[crzycav86]

Are your HC and CO good? If not, it may be your cat. If your HC and CO are really good, you can try retarding the timing. Also, if you suspect that your engine has a lot of carbon, you may want to run a seafoam treatment to lower the pressure of the combustion chamber.

This sums up what I've learned about NOx from searching the nissan mechanics forum... It may help you as well to do the same. Good luck