The engine is a b20, there is no smoke from the exhaust, the smell is like rotten eggs. The engine has no oil leaks and doesn't burn any oil. I've replace the cat converter, the spark plugs(even though the old ones looked okay and seemed to be burning alright), checked resistance in plug leads, the engine is running smoothly but I am getting poor gas mileage. I've done the tappets and there isn't any leaks in vacuum hoses.There is no engine warning light showing, I've checked the ECU and there are no codes coming up on that. Any ideas what could be causing the smell?

 

Rotten egg smell is usually a bad cat converter...

 

or a sign that you have a really heavy foot lol