On 8 Dec 2004 12:47:20 -0800, "old school bmw owner"
> wrote:

>1986 BMW325e 178,000 miles:
>First test: FAILED NOx [actual=3.4829(gpm)cutpoint=2.8000(gpm)].
>So I changed oil and oil filter,spark plugs and air filter. Ran a full
>tank of gas with a bottle of Guaranteed to Pass and put a bottle of
>Heet in tank before retest with Chevron 87 octane gas. I ran the car
>for over 1/2 hour before retest to get it hot.
>
>Retest results: FAILED NOx [actual dropped to 3.0586(gpm)]AND
>FAILED HC [actual=2.0497(gpm)cutpoint=1.8000(gpm)]

I posted about this a few weeks ago...NOx is reduced by cooling down
the engine (which is what coolant does) and also cooling down the
combustion process (which is what EGR does). Flush the cooling
system with coolant flush and distilled water, clean the EGR system,
and if all fails the rhodium catalyst that converts NOx to nitrogen
and oxygen in the catalytic converter is probably shot. Plugs, o2
sensor, etc. have little effect on NOx.

IMHO NOx also gets worse in colder weather...I'm still working on
proving why, it's just a hypothesis right now...my best times for
inspection were always when temps were in the 60s or 70s F...winter
weather was always a disaster for my emissions.

Try checking your O2 sensor to make sure it's still working.

Dan