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#1 |
![]() Join Date: Nov 2013
Location: San Jose, CA
Posts: 132
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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!
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1991 ZR-1 #405 (white/black with blue pin stripes) |
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#2 |
![]() Join Date: Feb 2014
Location: AZ
Posts: 860
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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.
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#3 |
![]() Join Date: Nov 2013
Location: San Jose, CA
Posts: 132
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Nope. I had the key in my pocket.
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1991 ZR-1 #405 (white/black with blue pin stripes) |
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#4 |
![]() Join Date: Feb 2014
Location: AZ
Posts: 860
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#5 |
![]() Join Date: Apr 2004
Location: ATL. GA.
Posts: 2,168
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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?
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Steve 1990 Steel Blue/Black #2355 1990 Red/Red #1473 1991 Quasar /Black #118 Sold 1991 Turquoise/Black #766 Parted Out 1993 Yellow/White #179 Sold 1990 Black/Gray #1361 Headers/4:10s Sold |
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#6 |
![]() Join Date: Feb 2011
Location: San Marcos CA
Posts: 1,802
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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. |
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#7 |
Join Date: Jun 2013
Location: Toronto
Posts: 782
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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.
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#8 |
![]() Join Date: Aug 2009
Location: Livermore, Ca
Posts: 203
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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.
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1990 ZR-1 #642 |
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#9 |
![]() Join Date: Nov 2013
Location: San Jose, CA
Posts: 132
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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.
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1991 ZR-1 #405 (white/black with blue pin stripes) |
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#10 | |||
![]() Join Date: Nov 2013
Location: San Jose, CA
Posts: 132
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Quote:
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?
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1991 ZR-1 #405 (white/black with blue pin stripes) |
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