A cat that's had oil through it will be knackered, I assume you have looked at the lambda, esp if this came from the car with knackered rings as oil will also kill these.
Maps when they fail usually stick at a certain point, usually rich, possibly a safegaurd.
Check the map values, if they are changing on signal wire like they should then it's liklely to be ok.
Are all the plugs black, checked air filter, and fuel pressure ?
tabetha