the cap is there for setting the mixture.  that screw in your AFM that you
aren't supposed to play with.  you don't measure it after the cat because
the concentrations have changed due to the function of the cat.  few if
anyone uses a CO meter as far as i could tell.  the last time i had a car
tested a couple of years ago at the local dealer there was only one old
guy that knew how to operated the machine and it was rarely used.  i had
to wait until the day that he worked before they could do the test.  this
dealer does VW, Audi, and Porsche all in the same shop.

perhaps it is a bigger deal in states that have stricter emissions
testing.  basically here on modern cars which is what most shops work on
they just use the OBD II or newer version to test the function of the cat
with the two oxygen sensors one before the cat and one after the cat.
this is why the shop no longer knows how to use the CO machine.

jonathan

On Fri, 1 May 2009, Rob wrote:

> At  4/30/2009 07:13 PM, David Beierl wrote:
>
>
>> Sounds as though S&S weren't thinking very clearly.  You'll need to
>> get a test bung welded on...you absolutely have to measure upstream
>> of the CAT because one of its main functions is converting 2CO + O2 -->
>> 2CO2
>
> I was not aware that anyone actually ever pulled that cap. If the cat
> is not working properly wouldn't what's coming out of the tailpipe show that?
>
>
>
> Rob
> becida@comcast.net
>
>
>