Why smell like fireworks and running rough?

Hi:
The catalytic converter will make that smell. If you hear a ratteling, something tells me internally it has come loose and is plugging the system.

When the engine is cold and you can safely get under the car, take a rubber mallot and tap in the converter to see if that is where the noise is coming from. I have to add that even the muffler or resinator plugging up will cause the issue, so see if you can identify where it is coming from.

You mentioned, "what things can I check?" Based on your description, I feel you are correct. You didn't mention the color of the smoke from the exhaust which can be informative. If it is white, it could be coolant getting into the combustion chamber. That can destroy the convert too. If it is black, it could be a rich fuel mixture which can do the same.

Check the converter first. If it is good (and should be tested for back pressure to confirm) then we will need to check for ignition or fuel related problems. NOTE: If the check engine light was on, get a scanner and check for trouble codes. That can be very helpful in diagnisis. Most parts stores will lend you one.

Let me know if this is helpful. Sorry for being so wordy, but I'm trying to be as specific as possible with your info.

Take care and good luck,

Joe

Let me know what you find with the exhaust. The white smoke has me concerned that it could deal with a head gasket issue.

I'll wait for you response.
Joe

Glad to help. Let me know what you find.