There are a few mays you can do it.  Cats run at a very spacific temp
range.  Outside of that they will eventually melt or get plugged.  If your
O2 sensor dies the oxygen content of your exhaust changes and so does the
temprature therefor killing your cat.  Cranking without starting I don't
think will quickly kill the cat bacuase they are designed to take a small
amount of abuse when you start you car up.  Usually the cold start feature
makes the mixture richer for a few minutes and this won't kill the cat.
Prolonged driving at the wrong temp will kill it.

At 00:48 5/10/98 -0700, Joseph Tu wrote:
>Hello,
>
>I was wondering how you can mess up your cat. conv. Will cranking the
>engine over repeatedly without it starting mess up a cat? All possible
>ways, please do tell.
>
>Thanks,
>
>Joe
>
>

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