Re: running rich under boost (long response)

[PDQSHIP@aol.com]

In a message dated 95-10-05 21:04:51 EDT, you write:

>Subj:	re: running rich under boost (long response)
>Date:	95-10-05 21:04:51 EDT
>From:	Scott=John=Mockry%Mktg%TM@banyan2.BV.TEK.COM
>Sender:	quattro-owner@coimbra.ans.net
>To:	quattro@coimbra.ans.net
>
>Nick,
>
>When you mention you are getting a "running rich" smell what do you mean
>exactly. Are you
>smelling raw fuel/gasoline while under boost or are you getting a sulphur
>smell? I believe
>the sulphur smell is actually caused by running the engine/cat convertor
>slightly lean for
>long periods  and then under a rich condition (ie going up a hill under
heavy
>load) the sulphur
>smell is produced.
>
>With the fuel system in closed loop operation the O2 sensor voltage cycles
up
>and down between 
>0.1V and 0.9V as the engine computer  senses the O2 voltage and then changes
>the frequency valve 
>duty cycle. You can watch the frequency valve signal duty cycle change back
>and forth on an
> oscilloscope and if you connect up the O2 voltage signal on  channel 2 of
>the scope you will
> see how the high (rich)  O2 voltage will  cause the frequency valve duty
>cycle to change in order
>to  lean out the mixture. Then the O2 voltage responds to this lean
condition
>and goes low  and 
>then the frequency valve duty cycle will change again to richen up the
>mixture 
>(only small changes in mixture are occuring). This toggling back and forth
>rich and lean actually
>allows the 3-way catalytic convertor to oxidize Hydrocarbons and CO and to
>reduce NOx.

+++++............
>
Great post.......  Now peak power will occur at about 12.6 to 1 A/F......
 The prollum is exactly what the post was about......  If you run this rich
for any length of time you WILL burn up the cats innerds, and depending on
how you look at it, this can be a bad thing.....  With the stock exhaust the
chunks will clog the mufflers......  With a flowmaster, you deposit the
honeycombs on the track at, oh, maybe, Brainerd........    Sounds to me like
if there is smell coming from the cat, you have a prollum with too much
rich......  So, Control Pressure is too low at operating temps, or you have a
faulty lambda circuit (O2 or O2 freq valve), or you have a too rich warm idle
setting.......  That's all it could be for rich.......   And, BTW, a good O2
will hold a DC with not much variance, and a bad one will swing in a 5-10%
range when trying to set at idle.......  If you are too rich at idle you
should have the lambda out of the circuit (you can hear it in the FD), cuz
the lambda will not operatebeyond a certain rich condition, cuz it's trying
to decrease the DC beyond its given perameters, and you just won't hear the
FV anymore........

HTH

Scott