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Re: MC engine, catalytic converter removal



At 09:27 99-08-24 GMT, Phil Payne wrote:

>Checking Family Pictures, I find that the OXS sensor for the MC engine
>is mounted in the front of the cat.  On the car I'm looking at, the
>cat has been removed - so this begs the question of what happened to
>the OXS sensor.

My '87 5KT fwd has the O2 sensor mounted in the downpipe, right after the
turbo.
However, FP shows that on all '90 turbo models (both fwd and quattro) the
sensor is indeed mounted in the cat. They probably moved the location of
the sensor at the time when they changed the design of the cat (early
models have round cats, while late cars have flat-looking ones).

>Hmmm.  I'm assuming that the ECU is a MAC-11 (single knock sensor). And
>it _does_ damn well need OXS sensor input to keep the mixture right at
>cruise.  We all know the symptoms of a dead OXS sensor, and this car is
>probably showing them.  No wonder he's unhappy with the performance
>and wants to sell it.  Heh.

As I understand it, when the failing O2 sensor symptoms are only apparent
when the sensor starts to fail (it's usually slow to react when the mixture
rapidly changes from rich to lean and vice versa). If the sensor is
_really_ dead or it has been disconnected the ECU will see that, generate a
fault code and switch to a preprogrammed mixture settings.

>Question - when youze guyz remove the cats on MCs, what do you do about
>the OXS sensor?

FP indicate that the p/n for the downpipe is the same through model years -
443 253 101AS. Even if the sensor was originally mounted in the cat and is
now missing, the downpipe should have a plugged hole for the O2 sensor.

--
Aleksander Mierzwa
Warsaw, Poland
87 5KT

PS. It's my first post to the list since maybe, well, 6 months? I hope you
folks still remember me ;-)