Don't just watch for those symptoms. For the sake of your safety and
that of other drivers who would be endangered if you pass out behind
the wheel, please get your exhaust system checked and repaired right
away. It's not worth the risk to wait it out.

The symptoms are extremely sneaky.  A friend couldn't understand how
come he couldn't stay awake for highway driving until I drove with him
and realized the soft top on with no windows in it was a CO trap.  No
smell at all but I got that headache right away.  Once he realized he
had to have the front door windows open as well, we were ok.

You can use an old chunk of garden hose or some other tube and hold one
end to your ear while moving the other end around the manifold area.
Inspection techs have a stethoscope type thing for doing that.

If the exhaust is recently new, I would be suspecting the fitting where
the manifold hooks to the pipe as being a likely place something came
loose or shifted causing a leak.  Black streaks are also a give away.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Start the car. Have your buddy hold a towel or thick rag firmly over the
tailpipe(s) to build up some pressure. Not TOO tight... don't want the
muffler(s) to explode. :)

Listen for whistles or similar noises where the exhaust is leaking out.
If you can reach, hold your hand near the various joints and feel for a
rush of exhaust from the leak.

Don't burn yourself, and stay away from moving parts (fan, belts).