So i go to get my car smogged 1991 civic sedan hella clean only 133xxx miles and it fails the NOx test pretty bad too.
the car was tuned up before i bought it plugs/wires brand new dizzy ,alt. new cat i take the car back and we change the oil and seafoam it before.
anyone know what controls the nox output and how you can lower it?
i searched thru google and asked multiple mechanics so any advise could help.
thanks!

 

Nox is created by high combustion temps, above 2500 degrees.

There are a few reasons it is created in motors...other than normal.

High compression (carbon deposits)
Lean condition (Bad o2 sensor, vacuum leak, poor injector flow.)
advanced timing
Bad EGR valve (if equipted)or plugged EGR ports.
low fuel pressure
And a few more.

More than likely a bad o2 sensor if nothing has been done to the motor.
Honda recommends replacing them at 120K

 

thanks i forgot the o2 sensors are new
my model doesnt have the egr valve apparently i was thinking advanced timing thanks for throwing that out there or i probally woulda just thought it was a dumb idea!

 

apparently they are not new , replaced a wiggling dizzy rotor and cap still fail, o2's tomorow

 

How old is your cat. converter? That also helps lower Nox.

 

What are the NoX numbers you are getting (and what is the passing number)?

What ocatne gas are you using? For smog and noX issues you want the run the LOWEST octane without pinging. Also don't put ANYTHING in the gas when you test. Injector cleaners and additives often mess up your NoX.

 

timing will cause nox too if its too advanced.
im guessing ur motor is a 1.5l non-vtec?
if it is, ur timing spec is 18 degree +- 2 degree's
try to get it to 16 degree's
but we really need to know your readings first to really get an idea where to point u to.
HC:
CO:
Co2:
nox:
15 mph reading:
25 mph reading:

how old is your cat?
o2 not a bad idea but how old is it and how do it look like???
is there white flakes on the o2??
u might want to get a IAC gasket and carb clean and take your IAC off and clean it.
carbon build up is common there.
um..... cant think of n e thing else atm....
oh if u have a DPFI take the cover off where the intake tube goes to and take the spliter plate off. * it consist of 4 phillips screws that hold it on. black cover*
imo that's a restriction, and can cause a lean reading. my .02 cent.