Exhaust stink

[Programmer]

Ha--put my foot in my mouth again. H2S it is <g>...Good thing I'm not a
chemist....just browsing through some old TSB's on the subject--repair was
to relocate the O2 sensor so it read off BOTH sides and replace the PROM.
Basic problem was richness at idle...

Lyndon.
-----Original Message-----
From: Rudi Machilek <Rudi at vnet.net>
To: gmecm at efi332.eng.ohio-state.edu <gmecm at efi332.eng.ohio-state.edu>
Date: November 1, 1999 4:16 PM
Subject: RE: Exhaust stink


>The stink is Hydrogen Sulfide (H2S) not Sulfuric Acid (H2SO4).  The sulfur
>comes from the fuel (No sulfur in fuel or oil, no rotten egg smell).  You
>pretty well need a significant lack of oxygen (real rich burn) to make
>Hydrogen Sulfide. The catalytic converter has to be running rich also.  The
>problem is only evident when the catalytic converter is not yet lit or
>poisoned by lead.  The converter provides a great deal of surface area to
>promote undesirable reactions (Harder to smell rotten eggs from a non
>converter car).  Some designs are a lot worse than others. As soon as there
>is enough oxygen around at temperature, in either the combustion chamber or
>catalytic converter, one gets the various oxide forms instead.  These oxide
>forms are acid rain and smog problems, but do not smell like rotten eggs.
>At very high combustion temperatures (lean burn conditions), thermal NOx is
>formed and SOx is formed (in greater abundance) which when combined with
>water make Nitric Acid and Sulfuric Acid.  These are also valve burn or at
>least high EGT conditions.
>
>ECM content; work on fuel map to keep A/F ratio in range and EGT under
>control.  If running cats, keep air pump.  Rotten egg smell is not as much
>of an issue with newer ECMs with post cat O2 sensor.
>
>Kept most of the chemistry and thermo out, but I believe accurate enough.
>
>Rudi Machilek
>formerly Project Engineer/Manager under contract with EPA, both Stationary
>Sources and Mobile Sources, RTP, NC
>
>
>>> Whats the reason some vehicles STINK from unleaded fuel / cat
>>> convertors and others don't
>>> Geoff
>>>
>>
>