High nitrous-oxides on smog check - what could be the deal?

[george graves]

HC's were normal - but it's failing on the nitrous oxides. What could it be?

I think I might have a intake leak - I'm going to poke around the motor with some cold start fluid to see if I can dectect it...

Anyone know what it might be? - The smog guy thinks It needs a new cat - does the cat even do anything for NO's?

Thanks!

George

(89 325is)

[KenC]

Re: High nitrous-oxides on smog check - what could be the de

HC's were normal - but it's failing on the nitrous oxides. What could it be?

I think I might have a intake leak - I'm going to poke around the motor with some cold start fluid to see if I can dectect it...

Anyone know what it might be? - The smog guy thinks It needs a new cat - does the cat even do anything for NO's?

Thanks!

George

(89 325is)

If you search, there was a thread about this in Oct I think.

I had high NO2 and high carbon. I replaced the O2 sensor and the cat and it passed with flying colors. I got a new cat+downpipes from BavAuto for a good price.

I think the high NO2 means that you're running lean. How long has it been since you replaced your O2 sensor?

[george graves]

Just pick up the car a few weeks ago(the seller claimed the car had been smogged and passed) - I have no history on the car.

the O2 might be original for all I know (230k miles on the odo)

replaced the spark plugs, rotor and cap...the timing belt has been replaced, and the timing belt is aligned correctly(it wasn't when I bought the car) - did all this a week ago.

Drove the car hard and reeally heated it up before smog...Still have 1000 miles till the next old change.

Any advice?

[OldUser1]

I had the same problem trying to get my car to pass smog. My smog results brought up 863ppm of NO when 815 is max. Turned out to be a bad O2 sensor.

Edit: My cat is really clogged up so that gave it a hard time passing smog. I'm going to have to buy a new one next time I have to get my car smogged.

[DaN]

Oxides of nitrogen are created by high combustion temps, so anything that could cause the car to run hot, could also cause NoX.
One of the purposes of the cat is to reduce Nox, so a new one in this situation might help.
You may want to run some concentrated fuel injector cleaner, and change the oil. And don't get it super hot before having it tested, this may reduce other emissions but it will increase Nox.