[Diy_efi] Emissions Numbers...

[mbelloli at speedymotorsports.com]

Mike,
     I run these tests everyday here in Millbrae, California.  We're right
outside San Francisco.  In running these test all the time I've seen
that usually over-advanced ignition timing, or failure of the exhuast
emissions systems bring about Nox failures.  And We replace a lot of
Catalytic converters.  The newer test really tests the ability of the
CAT where the two speed idle test really didn't.  When you say your
CAT is hollowed out - If it is considered a TWC - or Three-way Cat -
then one part of the Cat is for lowering Nox emissions.  On a lot of
newer vehicles the only thing lowering Nox is the CAT.  There is no
EGR system.  On big block 454's I've seen where everything was
running really good the Nox numbers before the Cat were around
1600ppms.  And after the Cat they were 200ppms.  On modified cars I'm
usually fixing problems with Ignition timing.  One more note, if you
are going really lean, you'll see a rise in HC, big rise, which you
aren't seeing here.




> Seeing as I have been having so much trouble getting the fueling straight
> on my new Vortec headed TPI engine I took my car to a local inspection
> stop today and got a treadmill emissions test. Here in Fort Bend county SW
> of Houston, Texas I learned they do a two stage test. One minute at 15mph
> and one minute at 25mph. Both runs in second gear. It's done twice with
> the best readings of both runs being the ones they accept and use. Even
> though I knew my car would not pass seeing as I still have not found the
> root cause of the idle/low speed 160 BLMs that I am getting I found the
> results interesting. BTW my car did fail. It flunked the NOx during the
> 15mph runs. Here are the results they handed me.  The CO readings are a
little lean, but I'm wondering if you had any air injection?  Normally
around .5-.6% before Cat.  That would account for the lower CO2, and
higher O2.  The higher the CO2 the better, always.  When everything is
right on this number is usually about as high as it can get. 14.7 is
usually as I as I've seen on American cars.  15% on hondas.  And O2
around .5%-1.5%.  Now these numbers are with cams up to about 270
duration.  AFter that it is anybodies guess.

Marcello

>
> 25mph:
> HC(ppm) std-148 reading-65
> CO(%) std-.94 reading-.36
> CO2(%) 12.9
> O2(%) 2.9
> NOx(ppm) std-1047 reading-660
> Dilution(%) std->6 reading-13.3
>
> 15mph:
> HC(ppm) std-152 reading-108
> CO(%) std-.86 reading-.37
> CO2(%) 13.3
> O2(%) 2.3
> NOx(ppm) std-1146 reading-1635(*FAIL*)
> Dilution(%) std->6 reading-13.7
>
> If I remember right high NOx numbers are usually a result of high
> combustion temperatures due to lean conditions. Seeing as my less than
> smooth idle feels like I am not firing evenly I am thinking that I may
> have an injector or two on the O2 sensor side of the engine that are
> either somewhat clogged or not opening properly at low speeds. Any
> thoughts?
>
> BTW anyone know what "Dilution" is?
>
> Oh yeah, one more interesting is that I received passing higher speed
> readings even though I have a hollow cat.
>
> Mike
> '86 Z28
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