Hmmmm .... this started out as simply wanting to get past emissions test, but got more interesting :-)


So, in summaary, between test 2 and 3, after new O2 sensor, retarding timing a couple of degrees, and end for ending the cat:

HC rose at 15mph, but went down quite a bit at 25mph
CO rose at both speeds/rpm.
NOx down at both speeds, but way down at 25mph.

OK, trying to figure this out, but not getting far .... looking at only the 25mph test, then: since HC went down means running leaner, but CO rose which means richer - opposite effects?

Some texts note that the cat provides a reduction in Nox when the CO increases...

Probably interrelated play, then? Faster sensor cycle (primary), maybe the cat (secondary), and maybe some effect from the timing (tertiary)?

Thanks very much for your assistance, David ... now am sell this thing (although it does have a nice sound between 6-7000 RPM and spins very quickly. Gotta get to the next project - rebuilding the 1972 BSA 500!

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg