The following info may come in useful when you have failed
test (so I'm told.... 12RoT)
High HC - Hydrocarbons - Indicates a misfire condition (incomplete or
* 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).