1994 Honda Civic Q&A
1994 Honda Civic Question: How can I lower my High Speed Nox (ppm)?
ck egr passages for blockage of carbon or timing can be retarded or poss o2 sensor - globalhelper
Globalhelpers suggestion first!! EGR SYSTEM function is very important. Next would be timing as he mentioned , and then be sure the cooling system is in good shape. Last , if high miles (by age I'm assuming it is) maybe a top engine cleaner -get carbon build-up off pistons -lower comp. lower combustion temp=lower Nox. - ziptie12
Check EGR, and Carbon build-up - your.mechanic