I have a 95 LS teg with DC 4-1 header. carsound cat and OEM ITR catback and my gf has a 93 Civic EX coupe (bone stock) and both our cars failed emissions with high NOx readings. Can anyone shed some light as to possible causes for a high NOx reading? TIA.

 

dc headers are known for giving high emission readings. do u have any of ur stock equipment u can put back on?

did u warm the car up and keep it warm right before the smog test? how long have u had ur cat for?

 

Well the funny thing is..I had the same setup last year and passed emissions fine. I don't know what could have changed since then to make me fail now. Do any of the following have any effect on NOx readings?

- Bottom two pipes on header dented (stupid potholes )
- Possibly need a new cat?
- O2 sensor maybe?

 

NOx are caused by heat, usually N2 gas just goes in... and comes out but when it gets hot it reacts with oxygen... not sure exactly why your car failed, what about fuel mixture?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PhAtBoY Si &raquo;</TD></TR><TR><TD CLASS="quote">Well the funny thing is..I had the same setup last year and passed emissions fine. I don't know what could have changed since then to make me fail now. Do any of the following have any effect on NOx readings?

- Bottom two pipes on header dented (stupid potholes )
- Possibly need a new cat?
- O2 sensor maybe?</TD></TR></TABLE>


Uhhhmmm, let me see...

header, cat, O2 sensor, all emissions control products.

What do you think?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 2camsaam &raquo;</TD></TR><TR><TD CLASS="quote">


Uhhhmmm, let me see...

header, cat, O2 sensor, all emissions control products.

What do you think?</TD></TR></TABLE>

Well all of the above obviously affect emissions, but I'm wondering specifically how each affects the NOx levels. If I had a bad cat, wouldn't that cause me to have a high hydrocarbon reading rather than NOx?

 

Your cat has two types of catalyst:

Oxidation catalyst : Palladium & platinum to reduce hydrocrabon emssions.

Reduction Catalyst: Palladium & rhodium to reduce NOx emissions (converts to oxygen & nitrogen gas)

If your cat isnt working it will effect your NOx emssions as well as your Hydrocarbon emissions but depending on whats wrong with it not necessarily both... hope this helps, try another cat!

 

Converter is going bad - had the same problem from last year to this year.

 

OK guys..here are the exact reading from the emissions test. Tell me what you think:

NOx: 2740 Limit: 1372 (Too high - FAILED)
HC: 84 Limit: 173 OK
CO%: .34 Limit: % .97 OK
CO2%: 12.4
O2%: 2.7

Any ideas or suggestions?

 

BTW, those readings are for the bone stock 93 Civic EX coupe but the ones for the Integra are very similar. Any opinions guys?

 

ttt anyone please?