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Originally Posted by tino
After miserably failing the clean air test one day then passing the next day after only increasing the idle .
The First test results which FAIL were as follows :
at curb idle 678 RPM
HC -- limit 300 reading 650 -- CO limit 1.50 reading 8.18-----
At 1644 RPM
HC-- limit 90--reading 334---CO--limit ,50-- reading--8.41 NO-- limit 979 -- reading 36
The strange thing to me is that just by increasing the idle a bit the HC, Co went down BUT the NO went up dramatically. PASS results as follows.
At 1671 RPM
HC reading 68---- CO reading 0.04 -------- BUT---------NO ppm went up to 354
I know at this point it's all just academic but are these cars so finicky ?
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NOx engine out is maximum at about 10 percent excess air, which is quite lean. As the mixture is richened engine out NOx declines. Once the mixture is richer than stoichiometric NOx drops rapidly due to its effect on cooling peak flame front temperature. Running slightly rich was actually an NOx emission control strategy back in the seventies. Then the high HC and CO was was cleaned up with air injection and a two-way (oxidation only) catalyst.
Your first test numbers indicate about 30 percent excess fuel - the engine was obviously not in closed loop mode. In fact, it appears that it was tested virtually stone cold.
Did you just drop off the car at some shop and come back later?
Your second test numbers indicate a properly functioning lamda system and a hot catalyst. The NOx went up because the mixture was stoichiometric rather than way rich, but it's only about one-third the test limit.
Duke
05-15-2005, 08:47 PM
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