Just Failed CA Smog. Now what?

[Okiedoke]

I bought my Z just over a year ago. Presumably it would have had to pass smog at that time. This time, everything passed except for NOX. Max for the 15MPH test is 545 PPM. My Z measured 587 PPM. The 25MPH test passed with 459 PPM. The Max is 502 PPM. The car is stock except for a KnN filter. I just went through some of the CA smog related threads and there seem to be folks who got a measurement in the 200s. In this thread by Z51JEFF, it looks like he passed by replacing his O2 sensors. Is this what I should try? If so, does anyone know what model and where I can get them and how many? Is there any way to tell after replacing the sensors whether it will work short of taking another smog test? Thanks!

[KILLSHOTS]

Did you have the power key in the FULL position during the test? If so, you may want to switch to NORMAL and run the test again. Ask me how I know.

[Okiedoke]

Originally Posted by KILLSHOTS

Did you have the power key in the FULL position during the test? If so, you may want to switch to NORMAL and run the test again. Ask me how I know.

Nope. I had the key in my pocket.

[KILLSHOTS]

Originally Posted by Okiedoke

Nope. I had the key in my pocket.

Nuts! Too bad it couldn't be something so simple. Good luck.

[We Gone]

Do you have the stock prom? Jerry's sells the O2's. Will the testers in Calf. let you run the test in a test mode to see if it will pass after you change the O2's?

[mike100]

additional ignition timing would elevate NOx, but usually the port throttle closed timing map at the lower rev ranges doesn't deviate from stock much on some tunes.

If the other numbers were looking good except for NOx you surely need new O2 sensors. Cleaned my car right up. I will need to see your exact results for a more specific diagnosis though. Another easy fix is if you have a bad vacuum leak under the plenum somewhere (you can tell by a high idle).

I got the oxygen sensors from O'Reillys- they have the proper length 3 conductor wire harnesses.

[5ABI VT]

Was the car hot when tested? have you given it a good run @ wot beforehand and clean oil? My SS failed ever so slightly.. I gave it balls to the wall for 15 mins and came back and it passed with flying colors.

[Coupe89]

First time I tried to pass smog. Failed 3 times. Changed Eprom/Chip. Passed.

Last year I failed too many times. lol

Changed out the O2's. Picked up a pair of Bosch at the local parts store. Failed
Had to change out a bad injector it had 8.8 ohm's. Failed.
Then shop noticed the key in full power. They switched the key and passed. For got about the key after I changed out the injectors.

15-518 25-452

My shop suggested to change out the cats.

[Okiedoke]

Originally Posted by We Gone

Do you have the stock prom? Jerry's sells the O2's. Will the testers in Calf. let you run the test in a test mode to see if it will pass after you change the O2's?

AFAIK, it's the stock prom. I haven't touched it at least. I doubt the tester will do a test pass. I do get a second official attempt for free within 30 days though.

[Okiedoke]

Originally Posted by mike100

If the other numbers were looking good except for NOx you surely need new O2 sensors. Cleaned my car right up. I will need to see your exact results for a more specific diagnosis though.

Yes. All of the other numbers looked good. Here's the report:

Originally Posted by mike100

Another easy fix is if you have a bad vacuum leak under the plenum somewhere (you can tell by a high idle).

Now that you mention it, I haven't heard that clicking sound indicative of a vacuum leak when I start the engine in a long time. How high is considered a high idle?

Originally Posted by mike100

I got the oxygen sensors from O'Reillys- they have the proper length 3 conductor wire harnesses.

I looked up both O'Reilly and Jerry's and found the following sensors:

1) O'Reilly: Bosch - Oxygen Sensor - Part#13077 ($45.99)
2) O'Reilly: Bosch - Universal Oxygen Sensor - Part#15726 ($57.99)
3) Jerry's: Delphi - Oxygen Sensor - OEM? GM PN 10137641 ($47.75)
4) Jerry's: Denso - Oxygen Sensor - GM PN 10137641 ($59.75)

Would all these work? Which is the preferred part?

Is this something I can easily swap out or should I take it to my mechanic?