What's up guys, I was wondering if you guys can help give me some thoughts on this little problem I have. My car is having trouble passing the nox emissions. Max should be 1077 and I'm getting 17-1800 on the cruise part of the test. The strange thing is originally when I first got it inspected it passed fine, although I don't have the sheet to compare and this was only a year ago. I had the recent test done before the tune and after the tune and the results are the same. I thought that having the car sitting for a while was the culprit but that's not the case. So basicly I'm looking for opinions on what might be causing the high nox emissions on a 7,000 mile brand new crate engine!! Hc and co's are fine, test vehicle is an 85 Monte SS. You figure a 20 year newer engine should pass with flying colors but that's not the case!

 

Generally, two things will increase NOx formation in SI gasoline engines: 1) increased combustion temperature, 2) longer burn duration.

Things typically done to reduce NOx:
1) NOx-reducing 3-way catalytic convertor
2) EGR to to lower combustion temp
3) Lower compression ratio to lower combustion temp
4) Fast-burn combustion chamber to reduce burn duration

Are you running stock cam, heads, etc?

Have you checked both cats to make sure they haven't disentigrated?

Tried putting the timing maps back to stock?

Checked for a bad injector?

 

Move to Northern Arizona...No inspections of any kind!! Don't need hoods, fenders, windshields, doors or bumpers.
Bill