When a catalytic converter is stolen, the automobile will give tell-tale signs. At ignition, the vehicle will make a roaring sound and get louder when accelerating. The vehicle may “sputter” while in drive with increased exhaust fumes and odd smells, such as rotten eggs. The “Check Engine” light may appear and drivers will probably experience a shift in the car’s performance and fuel economy. And, of course, without the catalytic converter, a failed emissions test is inevitable.