A rotten egg smell is associated with a failing (clogged) cataslitic converter. If you have a lazer temp sensor you can test if the converter is working properly. Test the temp of the exhaust both before and after the converer. The tempature should be considerally higher after the converter.
The shade tree test is to separate the exhaust before the converter and test drive the vehicle (being carefull to not damage any componets while aparating or driving the vehicle) If your drivability concerns and the rotten egg smell goes away the converter is failing.
The thing to remember, in most situations, catalitic converters do not commit suicide, the is usually an underling cause. Generally a poorly running engine allows raw fuel to make it into the converter which burns and damages the catalist material or engine oil and/or coolant gets into the combustion chamber, makes it's way to the converter and clogs it.
Therefore, replacing the converter may not solve your problem. It may just eleviate the symtoms for a while untill the new converter is plugged up by the underlying cause.
Here's an idea and a place to start, let me know if it helps.
Tuesday, September 15th, 2009 AT 2:47 PM