...and you can tell how little by looking at your smog-check slip.  As
a broad general rule, the newer the car, the better.

I've actually read about a few failed suicide attempts for this reason
-- guy wakes up in the morning, realizes he's equipped with neither
halo nor pitchfork and his car is out of gas, opens the garage door
and decides to live another day.  Either that or he's dead but the
coroner decides it was the sleeping pills and the big belt of booze
that did it, not the exhaust fumes.

Exhaust from a properly  functioning modern car isn't exactly *good*
for you, but it isn't the luridly death dealing stuff of the pre-smog-
control era.  In those days, exhaust could also kill you at one remove
by causing you to fall asleep at the wheel or somesuch; and who knows
how many people walked around for months with a constant low-grade
headache and tiredness that turned out to be low level chronic CO
poisoning from an exhaust leak.  (Malfunctioning gas appliances in the
home can do this too -- thus the increasingly common CO alarm.)

Piping it into the passenger compartment of a closed car might kill
the driver by creating an oxygen deprived confined space, but one of
the products of a cat converter is CO2 , an overconcentration of this
is what actually gives you the urge to breathe.  I guess that you'd
either leave the vehicle or roll down the windows.   In fact, you'd
probably notice  that something was wrong with the air well before
that,  since exhaust does still have an odor (and so do a lot of
catalytic converters!)   There's the increased noise too -- especially
if you took the exhaust from upstream of the tailpipe in order to If
the original poster is writing a murder mystery,   this has to be
explained away in some manner.

--Joe