Do you still have the pre cat sensor hooked up?
Do you know if you have a pre and post cat o2 sensor?
Sounds like you have a pre and a post cat sensor, Even if you instal the post cat sensor into the exhaust, you will always have a check engine light since the motor thinks your CAT has failed.
However, if you still have the pre cat sensor hooked up, I *think* the engine will run right, except for the CEL
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