Skip the auto shop - Our mechanics make house calls

Q: Definately coming from the exhaust system

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Purge Valve location in 2011 Ford Taurus

The purge valve on most vehicles will be located near the fuel tank. The best way to determine the location of the purge valve is to look online for what the part looks like on your car, then inspect near...

Q: Power steering doesn't working

Hi there. A common issue many owners of your particular vehicle face is the power steering quitting on them. Usually, it is accompanied by an alert on the Prius' multi function display. Commonly, the power steering module will be the...

Q: Blue smoke black smoke white smoke what do they mean

Hello. If there is blueish smoke coming from the exhaust, then that is an indication that the engine is burning oil. This can come from the valve stem seals or from the piston rings. It can also come from the...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...