not passing smog high NOx at slow speed

[flinxsl]

Hi,

I have a 1998 Integra LS.

I have failed my smog retest after running seafoam treatment and tuning the ignition system. Before I was failing based on high HC, but now I am failing on high NOx, which was passing before.

What is really weird is that the NOx measurement is all over the place.

15 mph - 1071 ppm (fail)
25 mph - 27 ppm (pass)

What could cause this drastic difference at the slow speed? I haven't changed the ATF in 40k miles, and I notice sometimes at slow speeds the transmission doesn't catch all the way and bogs down the engine. Could this have caused the smog test to fail?

I am just trying to pass smog doing the minimum amount of maintenance on it because my registration is coming up, so if the ATF needs to be changed, so be it, but I want to rule out having to do anything else before I spring for it.

Thank you for your reply

 

[j13]

Ok so you did a tuneup to the ignition meaning, plugs, wires, roter, cap?

Maybe your cat has gone bad?

 

[flinxsl]

Thanks for the response.

Yes I did those things: plugs, cap, rotor. Checked wires with an ohm meter and they were fine. How can the cat be bad if it previously passed on this test before I did this tune? Also it passes at the high speed. Can the cat still be bad if this is the case?

 

[jdmjim]

it could be, but turn your timing back for the test. NOx is from heat in the combustion chamber, if its too lean it will raise your NOx

 

[JCNOOGEN]

go buy denatured alcohol from home depot or whatever . dump it in there.. warm up the car.. and make sure the car is hot..

 

[Whiteman51x]

you did a seafoam treatment right? this means that you unplugged a vacuum line correct? check the line to make sure it is connected all the way, and has the clamp on tight and is not cracked

also check your other vacuum lines and where does your idle sit? could be a coolant pocket smewhere.

the reason is that unmeasured air (vacuum leak) will cause the car to run a bit lean, and go figure AT LOW RPMS like you are experiencing because there is high vacuum at idle and as the engine speed increases, the vacuum decreases and the leak becomes insignificant compared to the amount of air entering the engine at higher rpm's

also, poor fuel quality can contribute

and lastly, take your car on the freeway and RAIL THE F%$# out of it and take it straight there and you will have a better chance of passing due to the cat being at operating temps

 

[phatintegra]

Had this issue on my Jeep for many years, did full tune up, flush coolant, colder thermostat, replace cat and 02 sensor and it past.