effect of CAT on WBO2 readings?

[romans, mark]

And on my 87 Vet AIR is injected into the 2nd part of the cat.  The first
half is n0x reduction, the 2nd part is HC and CO reduction and at idle my wb
reads about 17 -1 afr when in closed loop.  (Post cat)
AT WOT it should read what the afr is because the AIR injection shuts down
at wot.
Mark

----- Original Message -----
From: "Bernd Felsche" <bernie at innovative.iinet.net.au>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, March 05, 2002 5:36 PM
Subject: Re: effect of CAT on WBO2 readings?


> rob files tapped away at the keyboard with:
>
> > How much (if at all) will a WB measurement change if the sensor is
> > placed post cat (tailpipe probe), as opposed to pre cat (header
> > bung)?
>
> Post-cat conditions are at lower pressure so the pp of O2 in the
> exhaust gas will be lower when compared to the reference in the
> Nernst cell of the sensor - that's the "switching" part of the
> sensor the controller tries to keep at around 0.45V by changing the
> pump current.
>
> The amount of oxygen doesn't change - it's not thermo-nuclear. :-)
> The O2 reading will change due to pressure effects and the sensor's
> relative sensitivity to the various exhaust gas components.
>
> The amount will depend on the exhaust gas conditions in situ.
>
> --
> /"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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