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Q: Definately coming from the exhaust system

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Nissan altima coupe 3.5, aftermarket exhaust and straight pipe. Recently when I'm driving I hear that the exhaust sound louder in the car than before, like there is a hole. I also smell something when I stand next to the tailpipe after I turn the car off. To me it doesn't smell like rotten eggs, just a fume. When I'm driving and the engine is revving at 2-3 rpms it sounds like a motor boat revving, except not as loud. Not sure what this is or where to go for reasonable inspection and repair.

My car has 90000 miles.
My car has a manual transmission.

Hi There, It sounds like you may have a catalytic converter that may be failing. The catalytic converter converts toxic exhaust gases into less harmful pollutants that are suitable to be expelled into the atmosphere. When the inside structure of the catalytic converter falls apart or fails, you may recognize a very strong fume smell. The reduction catalyst is the first stage of the converter and uses platinum and rhodium to reduce nitrogen oxide emissions. The catalyst removes the nitrogen atom from the molecule and frees the oxygen atom; the nitrogen atoms then combine, forming a nitrogen gas molecule. Platinum and palladium are the materials that form the oxidation catalysts, which is the second stage of the converter. This catalyst converts unburned hydrocarbons and carbon monoxide molecules into carbon dioxide by burning them, which combines the molecules with the remaining oxygen in the exhaust gas. Catalysts are substances that accelerate a chemical process without being used up. They are organized in a honeycomb structure because a honeycomb shape provides the maximum amount of surface area, allowing the catalysts to have more exposure to the exhaust stream and thus minimizing the amount of catalyst required. I would recommend having an expert from YourMechanic come to your location to diagnose and replace your catalytic converter.

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