<VV> No Corvair - GM Catalyst Replacement?

[jvhroberts at aol.com]

Actually, it's not the sensors, it's the thesholds set in the computer 
that are so tricky.

-----Original Message-----
From: Bill Elliott <corvair at fnader.com>
To: Sethracer at aol.com
Cc: virtualvairs at corvair.org; gyoungwolf at earthlink.net
Sent: Tue, 13 Jan 2009 7:26 pm
Subject: Re: <VV> No Corvair - GM Catalyst Replacement?










The OBDII sensors are so sensitive that often even replacing with a
performance aftermarket converter can still cause recurring codes...
seems to be more of an issue with European cars (which tend to 
routinely
set those "converter performance codes" with great regularity as a
matter of course...)

Bill

Sethracer at aol.com wrote:

>
>In a message dated 1/13/2009 3:48:17 P.M. Pacific Standard Time,
>gyoungwolf at earthlink.net writes:
>
>If  anyone has done a converter replacement on a late model GM vehicle 
(this
>one  is a Tahoe), please drop me a note. I am wondering about the 
impact on
>the  computer functions if the coverter is replaced with a straight 
pipe.
(Don't
> need advise that it is illegal as it does not belong to me and the 
owner is
>aware of that :-).
>Thanks,
>Grant
>
>
>
>The late model GM Computers have connections to a pair of Oxygen 
sensors,
>one before and one after the converter. On initial start-up, the 
computer will

>check to see if the oxygen sensor is there and providing computer 
input that
>says it is within the correct operating range. (Raise your hand if you 
are
>here). After operation begins and the catalyst begins to operate, the 
computer

>tests to see if the "after" O2 sensor is showing an improvement from 
the O2
>sensor located before the converter. If it doesn't, This will set a 
"Check
>Engine" light and set the appropriate code in the computer. At that 
point, the

>car will not pass a smog test.
>
>Not a "legality" statement, but I don't want to breathe his smog. - He 

>should get it fixed. The running of the car may not be too affected, 
because
the
>before O2 sensor is providing feedback to the fuel system controls. 
The system,

> however can make the car run rich at some point, because it is 
counting on
>the  converter to clean up it's exhaust. Removing the converter may, 
indeed
>cause the  truck to pollute a lot more than an older car. Seems 
strange, but
that
>is what  allows new cars to run so well.
>
>
>
>Seth Emerson
>
>C's the Day! -  Corvair, Camaro, Corvette
>
>
>
>
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