QuestionI have a 1991 Civic wiyh 204,000 miles on it. In Ohio we must pass an emmissions test. The state-run test has failed my car, saying the NO (nitrous oxide) level is too high (by about 50 ppm). What might I look for to correct the problem?
AnswerFirst off, your car must be running for at least 15 minutes in order to pass an emissions test. During the warm-up period is when you'll get the worst emissions.
You're probably thinking of NOx, or Nitrogen Oxides. An excess amount can be created by too much heat in your engine. When combustion is most efficient, you are producing the most heat (good combustion = high heat). So, when combustion is most efficient, you're producing the highest amount of NOx.
I am not sure how many "do-overs" you have with the inspection, but I'd try to find a mechanic that'll accept a "bribe" if you will, just to let you use his analyzer. That way you can see if you will pass or not.
If your engine is running lean, the pistons will get seriously hot. If you can richen the fuel mixture a little, then you've got less heat, which means less NOx. I'd reset the ECU, then go ON THAT SAME DAY to get it checked. What you've got is the computer trying to relearn your driving habits. By default it runs rich. Now, if they'll impound your car or something like that on your next failure, then don't try it, but if it's one of those 'try it till you win' things...go for it.
1. Try using a different type of gasoline. If you usually get inexpensive fuel, run a tank with Shell V-Power, maybe that's it.
2. On a hunch, I would reset the ECU.
3. Check the following components...O2 sensor, catalytic converter, PCV (positive crankcase ventilation) valve
4. Have an SAE certified technician inspect your car?
Good luck,
I'm interested in finding out exactly what it is.
B
