High NO level in Smog Check at 15MPH, no problem at 25MPH, What Causes this?

Our 18 year old Camry just barely passed California smog with a nitrous oxide level just below the limit (426 ppm with a 430ppm limit at 15MPH on the dynamometer). But at 25 MPH on the dynamometer it was at 170ppm with a max of 717ppm. Why would the NO be so close to the limit at 15MPH but so far below the limit at 25MPH?
I can go two more years now, but I think that in 2016 it will be over the limit unless there was some issue with the test.
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wrote:

This is just a guess, but I think the root cause is 18 yr old stuff.
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wrote:

the dyno - did they have the "big honkin' fan" blasting at the rad while it was running? NOx goes up quickly with temperature. Or too much timing advance - which would be worse at speed.
Too lean can do it too.
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On Friday, June 6, 2014 2:48:20 PM UTC-7, sms wrote:

My 99 Nissan Maxima GLE did not pass this year. First time!!!! I went to my honest) mechanic -- only one in U.S. -- but still had to pay a whole *** *load of repairs to pass the smog.
Dilemma: Whether to fix up car or.. ? CA pays people to junk non-complyi ng cars up to a $$ limit. State also helps a little on fixing car, if low i ncome. What to do, what to do? Bottom line: Take the CA junque money and put it toward price of something else? Too damn much trouble to go out on the use d car market and find something as good as Old Betsy. And who knows what wo uld lurk in the bowels of "new" car, only to emerge later.
Bit the bullet; glad I did.

Save your pennies in case you have to make the above choices!
HB
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On 6/7/2014 8:45 AM, Higgs Boson wrote:

I have an honest mechanic too, a relative, plus he specializes in Toyotas. But he's ready to retire and sell the business. From looking online, a high NO level could be a lot of things. A failing catalytic converter, excessive carbon build-up, or an EGR issue. None of those are excessively expensive to repair.
What's amazing to me is that after 18 years, the cost of new Camry LE has only gone up about $1000. When we bought the 1996 it was tad under $17K with an MSRP of $21K and an invoice of 18.5K. Now a new LE is a tad under $18K with an MSRP of about 23.5K and an invoice of about 21.5K. Yet the new model has a lot more junk, ABS, more air bags, etc. Toyota is selling cars for a lot more under invoice than in the past, despite constantly insisting that they are going to stop doing all the incentives.
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sms wrote:

I am old school, PCV, EGR valve(if the car has one), Catalytic converter...
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On Fri, 06 Jun 2014 22:19:31 -0500, Gordon Shumway

still tested clean as the day it left the factory.
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