If your engine is running too rich, you’re wasting gas and creating problems for your engine and exhaust system. Running rich will also increase the output of polluting hydrocarbons from your engine. If your engine is running too rich, you can end up damaging your catalytic converter, which will require an expensive repair to replace. Running too rich means that your engine is consuming too much fuel for the amount for air that it is getting. Another cause of a rich condition is that not all of the fuel is being burned in the combustion chamber.