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if you have the exhaust emissions light on then this means there's an issue with the post cat O2 sensor or the catalyst itself
Its quite possible that the cat has been damaged by the previous engine damage
If the car feels down on power then this would back this up as a damaged cat can collapse and block the exhaust
so I'd suggest to remove the O2 sensor thats closest to the engine and see if you can peer inside the exhaust to view the cat brick as it should be nice and even
if that looks OK then I'd say to consider replacing the second O2 sensor ( the 1 after the cat further down the exhuast)
and also consider using a bottle of this
as its good for cleaning up the o2 sensors , fuel injectors as well as the cat