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Smog test NO levels rise suddenly?

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Old 05-10-2012, 04:49 PM   #1
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Default Smog test NO levels rise suddenly?

Hi all,
I was took my car to get smogged and the tech didnt like my headers and failed me for them. I passed everything else just not for the headers. I came back with the paper work for the headers about a week later to show they were legal and so he agreed to smog it again. Well anyways this time it failed the emissions part. Previously, ~1.5 weeks ago, the NO levels were something like 250 with the max allowable being around 490 or something. Well this time they shot up to 760. What could have changed in a week to cause this big of an increase? I've noticed no difference when driving the car, the only thing I changed was the spacing of the ICM and the coil wire. Could the EGR valve be stuck closed? Any help would be appreciated. Thanks!
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Old 05-10-2012, 04:55 PM   #2
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do you still have the cats on there?
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Old 05-11-2012, 12:42 AM   #3
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yeah it got the single cat system (stock for 94-95) nothing has changed since 1.5 weeks ago
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Old 05-11-2012, 09:10 AM   #4
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Use some octane boost and drive kind of hard to the inspection station so the cat gets good and hot. Could be that the cat was a little cool.
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Old 05-11-2012, 06:47 PM   #5
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Come to America, leave Calif. we don't have those problems and besides everything costs too much there.
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Old 05-11-2012, 10:18 PM   #6
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Tennessee doesn't have emission testing (unless you go to Shelby County). Nevada sounds like a nice place, too. All the rich people are leaving Cali for it.
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Old 05-12-2012, 03:35 PM   #7
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Quote:
Originally Posted by LS1121 View Post
Come to America, leave Calif. we don't have those problems and besides everything costs too much there.
LOL if only that were possible I'm going to college in cali though so I dont have many options right now. And do you guys think it could be related to the cat? I thought it only took care of hydrocarbons? Apparently NO is only produced when the combustion chambers are above 2500 F?
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Old 05-12-2012, 05:04 PM   #8
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Well it depends on what you have done to the car. Considering an 1994 is an OBD I type vehicle. I don't know what type of Emissions devices you have on your car. When is the last time you changed your plugs? A good burn is always important.
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Old 05-12-2012, 07:20 PM   #9
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Quote:
Originally Posted by goldylocks View Post
LOL if only that were possible I'm going to college in cali though so I dont have many options right now. And do you guys think it could be related to the cat? I thought it only took care of hydrocarbons? Apparently NO is only produced when the combustion chambers are above 2500 F?
There are better colleges.
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Old 05-13-2012, 09:02 AM   #10
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Not exactly sure what kind of test they use for a pre-OBD-II car out there in Kali.
It's likely a ASM/IM240. Did they run your car on the dyno?

Well if you went up there after failure & they agreed to test it was it hot during the second test? Was there a difference in the manner the 2 tests where run is what I'm asking?

NOx/NO =nitrogen oxides .
They can be difficult to reduce & or chase down a root cause in some cases.
They can be affected by many factors, ambient temp, engine temp, fuel etc.
They can also vary quite a bit in measurements as you now see.

If the motor is running well & in fuel control, the EGR system operating correctly I'd look @ the the catalyst.
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Old 05-13-2012, 12:56 PM   #11
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High nox is from high combustion temps. The egr system, on cars so equipped, combats this by diluting/cooling the intake charge with gasses from the egr valve. It is a measured amount introduced at the appropriate time. If your egr system checks out, your catalytic(s) is the culprit.
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