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Old 06-17-2010, 12:48 PM   #1
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Default Just smogged -- NO(PPM) a little high...whatsit mean?

Just had my 1997 Mazda 626LX 2.0L 4 cylinder coupe smogged and all the numbers look great except for the NO(PPM) at 15MPH. The Max allowed is 467, average is 57 and I was 230. So I passed, but want to know what this might signify. At 25MPH the max NO(PPM) is 754, average is 50 and I was 4! Could they have gotten my measurement wrong or is it possible that from 15 to 25 MPH the results could be so diametrically opposed?

This car only has a bit over 22,000 on it and I'm driving it maybe 1000 miles/year. Haven't had it looked at for quite a while.
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Old 06-17-2010, 01:27 PM   #2
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NO - nitrous oxide (parts per million). the crazy variation leads me to believe a busted machine.
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Old 06-17-2010, 02:07 PM   #3
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NO is related to EGR system. Could just be gunked up and slow to open or something along those lines.
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Old 06-17-2010, 03:15 PM   #4
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My Trans Am registered around 2500PPM on NOx.
I know my EGR vacuum solinoid is fubared, but they are discontinued and I'm having to hunt one down.
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Old 06-17-2010, 05:41 PM   #5
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I would clean the EGR as suggested. Also may want to run some top end engine cleaner to help get rid of carbon build up. Especially on high mileage cars. Also, for smog checks, fresh spark plugs and be sure to warm the car up by doing about a 30 minute highway drive. This gets everything, including the cat converter up to specs and temps. Never take a smog test without it being fully warmed up. Do not shut engine off while waiting on line either.
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Old 06-17-2010, 06:13 PM   #6
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I would clean the EGR as suggested. Also may want to run some top end engine cleaner to help get rid of carbon build up. Especially on high mileage cars. Also, for smog checks, fresh spark plugs and be sure to warm the car up by doing about a 30 minute highway drive. This gets everything, including the cat converter up to specs and temps. Never take a smog test without it being fully warmed up. Do not shut engine off while waiting on line either.
Why? It's not going to cool down enough to affect anything even if the car sits for 30 minutes.

I have a 7 year old Maxima with almost 90,000 miles on it and it passed last year with no trouble at all.
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Old 06-17-2010, 06:37 PM   #7
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Why? It's not going to cool down enough to affect anything even if the car sits for 30 minutes.

I have a 7 year old Maxima with almost 90,000 miles on it and it passed last year with no trouble at all.
Not in my experience. Then again. I was dealing with a 15 year old cat with nearly 200k on it. Drove it hard to the smog place. It sat for maybe 10 minutes. Got it on the rollers, fail. Revved it a bit and it passed like a champ.

Same for a friend of mine and his cat was new. In fact, for him driving to the smog check place wasn't enough to get it to pass. I told him to drive on a freeway for a bit in 4th (5-speed trans). Did that and it passed clean as a whistle.
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Old 06-17-2010, 06:52 PM   #8
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Cat converters need to hit a specific temperature in order to "light off"
The conversion of emissions does not happen until it is hot enough.That is why on later model cars, the converter is as close to the exhaust manifold on the motor as is possible. It heats up much faster.

See link for more information

http://www.aa1car.com/library/2000/ic60032.htm

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Old 06-17-2010, 06:53 PM   #9
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Yeah, my current car has 3! On a freakin' 4 banger.
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Old 06-17-2010, 07:19 PM   #10
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Am I correct in saying, from the posts so far, that you thrash the ar*eout of the car before the smog test so that the CAT is hot enough that you will pass the smog test?
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Old 06-17-2010, 07:25 PM   #11
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Not in my experience. Then again. I was dealing with a 15 year old cat with nearly 200k on it. Drove it hard to the smog place. It sat for maybe 10 minutes. Got it on the rollers, fail. Revved it a bit and it passed like a champ.

Same for a friend of mine and his cat was new. In fact, for him driving to the smog check place wasn't enough to get it to pass. I told him to drive on a freeway for a bit in 4th (5-speed trans). Did that and it passed clean as a whistle.
You know, I've lived in California for 20 years now and I've never had a car fail smog despite not following ANY of your advice...your friends must drive old clunkers with issues I guess.
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Old 06-17-2010, 08:21 PM   #12
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You know, I've lived in California for 20 years now and I've never had a car fail smog despite not following ANY of your advice...your friends must drive old clunkers with issues I guess.
My dad's 96 accord failed smog. Replaced O2 sensors, failed again. Brought it to a shop with CA's consumer assistance program. They checked the EGR system and it worked fine, and they found that the cat was bad. Replaced cat, almost everything was eliminated.

181k miles when it failed smog.
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Old 06-18-2010, 07:05 AM   #13
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Don't know what to tell you Jules. I'm not one to argue over stuff like this but that's what I've experienced.

And, in keeping with your experience, my dad's old truck ('89 Toyota) had zero problems passing smog and I know he didn't drive it hard prior to testing.
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Old 06-18-2010, 09:41 AM   #14
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I dont think its the EGR or the CAT, my car just passed smog but was way high on NO readings too, like 90% of allowable, everything else was lower than 15% of allowable. And my car has no EGR system and a brand new CAT. I think its cause i burn oil but i could be wrong.
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Old 06-18-2010, 08:07 PM   #15
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Not in my experience. Then again. I was dealing with a 15 year old cat with nearly 200k on it. Drove it hard to the smog place. It sat for maybe 10 minutes. Got it on the rollers, fail. Revved it a bit and it passed like a champ.

Same for a friend of mine and his cat was new. In fact, for him driving to the smog check place wasn't enough to get it to pass. I told him to drive on a freeway for a bit in 4th (5-speed trans). Did that and it passed clean as a whistle.
Yeah, I've been told to get it good and hot. Yesterday, I had an appointment for 10:00 and I had only 10 minutes to get the car warm, not enough time to take it on the freeway. So, I drove there in 2nd gear (it's an automatic but I can manually choose 1st or 2nd), and at all the stop lights I put it in neutral and reved to 3500 RPM. I got nervous when the guy told me it would be about 45 minutes and the car was sitting there cooling off. I walked out to the car and asked him if I could watch and he told me "no, it will be ~25 minutes" and I sat in the waiting room. I think my acting antsy helped! It was a cheapo place ($42, OTD), and they won't do retests, so I wanted to pass on the first try. I figured it was worth the gamble.

I wonder if my EGR valve is sticky. If it didn't act right at 15 mph but was OK at 25 mph, that would explain the weird results.
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Old 06-18-2010, 08:09 PM   #16
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I dont think its the EGR or the CAT, my car just passed smog but was way high on NO readings too, like 90% of allowable, everything else was lower than 15% of allowable. And my car has no EGR system and a brand new CAT. I think its cause i burn oil but i could be wrong.
I don't burn any oil at all.
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Old 06-19-2010, 03:35 AM   #17
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I dont think its the EGR or the CAT, my car just passed smog but was way high on NO readings too, like 90% of allowable, everything else was lower than 15% of allowable. And my car has no EGR system and a brand new CAT. I think its cause i burn oil but i could be wrong.
Oil doesn't cause NO, NO is strictly a function of combustion temperature which has to be pretty high for that combination to form. The whole function of EGR is to mix in some inert gas from the exhaust which reduces combustion chamber volume and absorbs heat (since it just sits there and occupies space without participating in the reaction).

Oil would only get you on a visual if it was bad enough to be smoking. The sniffer isn't looking for oil, just HC, NO, and CO. Not sure if burned oil registers as increased HC or not though, it's not quite the same as fuel chains.

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Old 06-19-2010, 07:24 AM   #18
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I wonder if my EGR valve is sticky. If it didn't act right at 15 mph but was OK at 25 mph, that would explain the weird results.
Would a "sticky" EGR device possibly explain the wildly different readings for NO at 15 mph and 25 mph? Is there a cheap/easy fix?
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Old 06-19-2010, 05:13 PM   #19
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Cat converters need to hit a specific temperature in order to "light off"
The conversion of emissions does not happen until it is hot enough.That is why on later model cars, the converter is as close to the exhaust manifold on the motor as is possible. It heats up much faster.

See link for more information

http://www.aa1car.com/library/2000/ic60032.htm
Absolutely correct. I tested catalytic converters in a dyno lab for 2 years in a previous life. They cool down very quickly, because the substrate is a ceramic that doesn't retain heat well. It also takes 20-30 seconds for a downstream large cat to light off, and 5-15 seconds for the smaller 'pup' converters that are up against the exhaust.

The start up period of your car is the single most polluting time for your car, and can equal many miles of fully warmed up driving.

In addition, there are some (few) cars that have hydrocarbon traps. These catch the initial gush of hydrocarbons and then release them when they reach temperature. You don't want them releasing during your test if you can avoid it, so keep those puppys at operating temperatures.

Gosh I'm glad I'm not in the exhaust business anymore =).
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Old 06-19-2010, 05:15 PM   #20
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Oil doesn't cause NO, NO is strictly a function of combustion temperature which has to be pretty high for that combination to form. The whole function of EGR is to mix in some inert gas from the exhaust which reduces combustion chamber volume and absorbs heat (since it just sits there and occupies space without participating in the reaction).

Oil would only get you on a visual if it was bad enough to be smoking. The sniffer isn't looking for oil, just HC, NO, and CO. Not sure if burned oil registers as increased HC or not though, it's not quite the same as fuel chains.
Nox formation, as you said, is a function of temperature. That is a function of air/fuel ratio, which is usually a function of O2 sensor function. If you're not pulling a code on the sensors though, I don't think that would be the issue.
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Old 06-19-2010, 07:28 PM   #21
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http://www.castlepackspower.com/Page...es/RSGDAN.html
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Old 06-21-2010, 08:17 AM   #22
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Terrific link. Thanks!
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Old 06-21-2010, 09:26 AM   #23
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I'm not a car guy, but one of my environmental chemistry textbooks said nitrogen oxides were created when the fuel mixture is lean. On the other side of the graph (rich) it would shoot out unburned carbon.

A random thought of what might work would be to run a richer fuel mixture to eliminate the NO then check if the catalytic converter is working properly since that is what eliminates unburned carbon.
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Old 06-21-2010, 10:31 AM   #24
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My 1990 240sx passed smog without any issues. Has 245k miles on it.
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Old 06-21-2010, 10:16 PM   #25
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Why? It's not going to cool down enough to affect anything even if the car sits for 30 minutes.

I have a 7 year old Maxima with almost 90,000 miles on it and it passed last year with no trouble at all.
Your 7 year old Maxima has 3 decent sized cats, and an efficient motor, you're citing a bad example to help your case.




Good link obamanation.
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