When a catalytic converter goes bad the car may be hard to start, the engine may have poor acceleration, the engine may use more fuel, produce dark exhaust and there may be excessive heat under the car.
Some ways you can tell if your catalytic converter is bad include.
Sluggish engine performance.
Reduced acceleration.
Dark exhaust smoke.
The smell of sulfur or rotten eggs from the exhaust.
Excessive heat under the vehicle.
The smell of sulfur or poor engine performance, decreased fuel mileage etc can all be signs of a bad catalytic converter.
Also failing a smog test can be an indicator of a bad catalytic convert that needs replaced.
The most common symptom of a bad catalytic converter is the smell of sulfur or rotten eggs from the exhaust and also excessive heat under the vehicle.
Sluggish engine performance, engine hesitation, loss of engine power, rough running engine etc are all signs of a bad or clogged catalytic converter.
If the catalytic converter is just slightly clogged then using some catalytic converter cleaner in your gas tank can help clear the clogged catalytic converter.
However if your catalytic converter is much more severely clogged then the catalytic converter would need replaced instead of cleaned.
It's recommended to use Catalytic Converter Cleaner every 2 fill ups of gasoline.
This will help keep the catalytic converter clean and prevent the catalytic converter from becoming clogged.
When you're using catalytic converter cleaner that you pour into your gas tank it's recommended to add a bottle of catalytic converter cleaner to your gasoline tank every 2 or 3 fill ups.
There's really no need to use catalytic converter every other fill up but it won't hurt anything if you do.
The catalytic converter cleaner helps to clean carbon deposits out of your exhaust system as well as the catalytic converter.
Catalytic converter cleaners that you pour into your gas tank and mix with your gasoline works to clean the catalytic converter as well as the rest of the exhaust system.
The catalytic converter cleaner works by burning in the combustion process and then cleans the carbon deposits out of the exhaust system and catalytic converter.
If you use catalytic converter cleaner every few fill ups of gasoline the catalytic converter will last longer and your engines fuel mileage will improve and your engine will run properly and better.
However if your catalytic converter is severely clogged then the only thing you can do is replace the catalytic converter with a new one.
If your state doesn't do emission testing then I would just recommend removing the catalytic converter and not replacing it.
I had the catalytic converters removed from my vehicles and they seem to run better and I don't have to worry about clogged or failing catalytic converters.