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The measurement for emissions tests is after the cat. A good cat will
take a fairly high CO% (1.5%) and reduce to levels similar to this
Honda's readings. For fuel mixture adjustments what is important is the
CO% ahead of the cat. I tend to set most Audi's to about 1.0-1.2% in
open loop mode. Using a 4 or 5 gas analyzer after the cat some people
can tell if the correct mixture is going into the cat and how well the
cat is working, I am not that well versed in 4 gas analysis. I have
found that the cat seems to reach a saturation point at which it seems
to quit working. Up to about 2.5-3.0% ahead of the cat I get about 0.5
after the cat, at 3.0-3.5% ahead of the cat I get 2.5-3.0% after the cat
just like it shut itself down. these were of course not scientific
studies with control groups and such just my recollection of my
observations over 17 yrs working on cars full time. Now they are just
thing I work on in my spare time.
Jim Dupree
1984 4ksq
1984 4ks

>From: 	Linus Toy[SMTP:linust@mindspring.com]
>Sent: 	Wednesday, November 19, 1997 3:18 PM
>To: 	quattro@coimbra.ans.net
>>From: waves@epix.net
>>Your Fox, running at those numbers must be running 
>>quite lean. To be running .06 on CO when the factory 
>>suggest .75 (at the test port) is def. a little off. 
>>You might loose half that after the cat, but .06 is real low.
>please explain...I am holding in my hand the recent Vehicle Emission Test
>Report for our '89 Honda Accord SEi (still for sale--anyone?)  This is
>Honda's 2.0L 4-banger with PGM FI system.  Car is absolutely stock, 90k
>miles.  At idle (760 rpm) it put out 0.02% CO.  Loaded cruise (on rollers),
>it still put out 0.02% CO.  In both cases, CO limit is 1.20%.  HC emissions
>were 7ppm idle, 2ppm cruise (220ppm limit).  As I recall, this car (as have
>a few others we have had for some time) regularly tests this low on CO.
>Yes, a low CO indicates complete combustion--but does that necessarily mean
>too lean? 
>* linus toy                       email:  linust@mindspring.com      *
>* mercer island, wa                                                  *