A CO detector will certainly let you know.
If you don't have one, start up the engine and look into the engine compartment right away. It takes a few minutes for the engine components to get warm enough to burn off any crud so if it happens right away, there is a good chance that it is an exhaust leak. Another thing is a well tuned ear can hear an exhaust leak.
Having an exhaust leak is a serious safety issue so be careful when you are troubleshooting. Keep all your hatches open and try to have a friend be there but standing in the cockpit where they can see you but won't get fumed out. The trouble with combustion gases is that you never notice that there is a problem which is the reason you want your friend standing somewhere else so they can see when you get loopy. Also, if you get lucky this friend might even have a good nose and ear.