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1995 Nissan 200sx with manual transmission and high mileage failed smog check for high HC, CO, and NOx.

I have a smog check due by early April. On 2009 smog check, it measured 91 PPM HC at 15mph, and 57 (the allowed max) at 25mph. CO was .24 & .18, somewhat high. The NO was 459ppm and 344, pretty high. I am looking for an inexpensive way to improve chances of passing check this year. I planned on new PCV, air filter, oil change, spark plugs (need wires too?), cap/rotor, and maybe removing & sending the injectors off for a thorough cleaning and rebuild. Would injector cleaning assist greatly with HC's? Or should I test for sufficient spark? Or both? Mileage is somewhat down, not terrible. Performance roughly normal; Slight stumble on acceleration. I see no obvious symptoms of plugged or damage CAT. I plan to check for vacuum leaks and clean EGR system and intake.
Answer:

Usually when emissions are high across the board such as in the case of your 1995 Nissan 200sx, the CAT is the culprit. However it's very important that you make sure there are no other emission problems. The repairs you mentioned will absolutely help lower emissions overall. Cleaning the injectors would help lower HC only if your vehicle was failing from a rich misfire, which it looks like it might. posted by SmogTips Support

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