>>>I think the idea was to reduce a target component of emissions. NOx I
>>>think... There was definitely a trade off made to reduce certain
pollutants while allowing some others to increase.<<<
That is pretty much it - back then. I can remember the guy at the gas
station smogging my first car back in 1976 (Datsun 510). He would turn the
idle mixture screw and as one level (CO I think - maybe NOX???) went up the
HC would go down and visa versa. The agony was that even at the most
balanced setting one or both were still out of range. :-(
From my understanding the HC can go up if you are too lean. Seems strange,
but apparently there is not enough fuel to adaquately burn the mixture. That
unburned fuel from the lean condition creates high HC reading.
One thing that people often say is to put Premium fuel in the car before the
test. Some indicate it is an old wives tale. Since NOX is typically formed
from a combustion chamber that is too hot there might be something to it on
a car that has high NOX levels. If the Premium lessens the liklihood of
pinging under load I would think that NOX could possibly be lowered in a
marginally failing car.
Something else to remember is that the smog laws typically require an
unmaintained car to pass even after 10's of 1,000's of miles. Thus, I'm sure
they have to overshoot the regulations from the start.
Tom
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