We have to know what amount of CO your Corvette produce. This will tell us
whether the cause of the high NOx is due to a lean fuel condition or not. If
CO is very low (0.00 to 0.05) your Chevy Corvette may have a fuel management
problem; maybe a bad oxygen sensor/s, mass air flow meter, pressure sensor,
or possibly clogged fuel injectors. These components will have to inspected.
If CO looked good (near average specs) you want to concentrate on the EGR
valve and EGR system. Your Corvette's EGR valve is responsible for lowering
NOx by re-circulating a small amount of exhaust gas (inert gas) back into
the combustion chambers. Nitrous Oxides (No) emissions are formed when
combustion chamber temperatures rise above 2500F. Presenting an inert gas
keeps the chambers cool and reduces NOx.
Other problems that could cause your Corvette to produce high NOx could be
bad engine cooling, lean fuel condition (though a lean fuel condition would
be suspected if CO levels were super low 0.00 to 0.05, as I mentioned) and
high mileage which could mean there is carbon build up on the valves and
piston heads of your Corvette's engine increase compression and engine
combustion temperatures.
