Would You Be Able to Smell Gas if Your Car Had a Bad Exhaust Manifold?

A bad manifold gasket can ruin your whole day, especially on a newer car. Of course, all the classic problems can still apply — problems like an ear shattering racket, and dying when carbon monoxide fills up your car’s cabin. Nowadays, though, that gas is doubly dangerous because computer controls can change whether or not it has an odor of gas at all.
Smells
All engines send a bit of unburned gas through the exhaust system. This gas goes through the catalytic converter, which much like a furnace, finishes burning the majority of it. If you have a leaking exhaust manifold, you might indeed smell some gasoline, because the unprocessed gases are escaping before they get to the converter. It’s uncommon, though, unless the engine is running unnaturally rich to begin with. That assumes, though, the air-fuel ratio remains stable. Once exhaust gases start escaping, any number of things could happen at the oxygen sensors before and after the catalytic converter, depending on temperature, the existing air-fuel ratio and how the computer is set up to adjust or cycle the mixture. This makes the smell of unburned gas an unreliable indicator of an exhaust manifold leak on newer cars.