My girlfriend has a 1980 or something Honda Civic which won't pass
emissions. Here in California, there are three tests: HC, CO, and NO. CO
I'm pretty sure is carbon monoxide, and HC I'm pretty sure is unburnt
hydro-carbons, such as fuel and oil. That car passes both those two tests
with flying colors.
It fails the NO test, which I think is mononitrogen monoxide, or maybe nitrogen oxides in general. Any ideas on what would cause a car to fail this test?
excessively lean fuel mixture, ignition timing off spec, malfunctioning EGR system are three things things I can think of