Failed HC ppm and CO % emissions Inspection

Dave,

Those numbers point to incomplete combustion. I'd suspect the fuel/air mixture is too rich.

How long has it been since that car has had the spark plugs changed? Also, is the O2 sensor in the rear exhaust manifold the original?

One other possibility - the catalytic converter may have reached the end of the road. Any competent place that does smog checks can do a propane test that will tell you if the converter is tired. If that car has the original converter and it has more than 125K miles, I'd have that converter capacity test done and see what the results are. That way you'll have some kind of idea what you're up against (seeing that replacing the converter is much more expensive than plugs or the O2 sensor).

Regards,

Bill Bowen Sacramento, CA

How do bad plugs cause higher CO? I thought they affected only HC.

Miss fire causes increase in manifold pressure, increased manifold pressure = higher MAP voltage, higher MAP voltage = richer mixture.