How do you know which coil is bad on a 99 Monte Carlo if the car has a coil pack?

AnswerLightly spray the exhaust manifold with water as the engine is running A good cylinder will evaporate the water quickly The misfiring cylinder will not. Replace the coil at the other end the spark plug wire from the bad cylinder

You can remove the suspect coil and switch it with a good coil and see if the two cylinders that were firing are now misfiring and the two that were misfiring are now firing.

If the coil pack is not working correctly then your car will be sluggish and should throw a misfire trouble code (check engine light). Usually only one coil will fail at a time. You can have the code scanned at autozone for free. They will also test your coils if you have them off the car. Always check your plugs and wires first before replacing the coil.