The following info may come in useful when you have failed an emissions
test (so I'm told.... 12RoT)

High HC - Hydrocarbons - Indicates a misfire condition (incomplete or
inefficient combustion).
         *  Ignition problems
         *  Carbon deposits in combustion chamber
         *  Overly lean A/F mixture
         *  Increased camshaft overlap

High CO - Carbon Monoxide - Indicates partially burned fuel (not enough
oxygen for complete combustion).
         *  Overly rich A/F mixture
         *  Dirty air filter
         *  High fuel pressure
         *  Dirty injectors
         *  Sluggish/inoperative Oxygen sensor
         *  Dirty oil

High NOx - Oxides of Nitrogen - Indicates excessively high combustion
chamber temps (such as produced during detonation).  Typically highest
readings found during part throttle/light load on non-detonating engine.
         *  Clogged/inoperative EGR
         *  Octane of fuel too low
         *  Compression (cranking pressure) too high

Things to do before going for emissions test if vehicle is modified or has
failed a test:

*   Fresh oil change.

*  New air filter (not K&N, you don't want the oil).

*   Run Techron through 12 gallons of fuel

*   Two to Three heat ranges hotter on spark plugs (for test period only).

*   Set idle up to 300 RPM over Mfg. specified idle speed.

*   Use higher octane fuel.

*   No vacuum leaks.

*   Set idle mixture slightly lean (too lean can increase NOx & HC).

Peter Schulz