They have a smog check for a vehicle with no smog controls that never had smog controls? In this country we'd call that crazy (and literally unconstitutional as it would be classified as an ex post facto law). Second, how do you have high CO2 readings? Do you mean high CO readings (incomplete combustion) or high hydrocarbon readings (really incomplete combustion)? CO2 is the final product in the combustion process. Its production constitutes complete combustion of the fuel introduced into the combustion chambers. If the only thing coming out of your truck's tailpipe is CO2, you can't have a better tuned engine.

58 Fleetside, 235, "The Old Buckin' Bronco"