Rotten Egg Smell from '95 S320

Catalytic Converter is ready for replacement.

Firstly, catalytic converters very seldomly need replacing. Replacing a cat is very expensive and to find you haven't cured the problem would be annoying wouldn't it. Let's look at what the smell actually is, why it is occuring and how best to address the problem.

The sulphur smell (rotten eggs) from the exhaust, is actually caused by running the engine (and therefore also the catalytic convertor) slightly lean for long periods and then running under a rich condition (I.E. going up a hill under heavy load). This is when the sulphur smell (rotten eggs) is produced.

Under relatively lean conditions, the sulphur found in petrol is converted to sulphur trioxide, then during the rich running condition the sulfur trioxide is converted into hydrogen sulphide (rotten eggs smell) within the catalytic converter.

The petrol / sulphur content of your brand of fuel and the characteristic of catalytic convertor to store sulphur compounds and release them during rich engine running conditions is the main cause of this problem. Switching petrol brands may help. The oxygen sensor may also need to be replaced to correct a fuel injection mixture problem.

Get yourself along to a garage that has a gas analyser and see exactly where your mixture is. Make sure this is right, and THEN start to look elsewhere. A gas check should only set you back a few pounds. If you're in the UK take the car to an MOT station, they have the equipment to check this problem out for you. Hydrogen sulphide stinks, I understand why you want this sorted out :) Mike

Switch gas station brand and drive more on highway to clear out the cat. It is usually continuous low engine speed that generate that odor.