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One way to determine the health of your cat/con:
If you have an infrared pyrometer similar to this $25 one
Amazing deals on this 12:1 Infrared Laser Thermometer at Harbor Freight. Quality tools & low prices.
You can measure the engine side of the Cat and compare it to the trailing side.
Here are videos from the stars of YouTube.
Google might provide other clues.
If you don't know if past maintenance has been done on a used car, you should check everything.
Pull a spark plug or two and measure the gap, verify it is at the spec on the emissions sticker under the hood. If the plugs are not the Iridium type, somebody cheaped out...replace them with Denso or NGK brands.