2003 Pontiac Aztek misfire

Are there drivability issues or just a code? Can you feel the misfire? Just about anything can cause a misfire, fuel--spark--compression.

Did you visually check for spark at that cylinder? If you have spark everywhere, check fuel--compression.

Sounds as if you may want to replace the coil pack. Try this, remove the two wires that go the coil pack for cylinder #6 (I think its coil pack 3 and 6). Remove them both and start the car. If you are getting a good strong spark then the two towers should arc to each other. If they do not, then I suspect a weak/bad coil.

Hope you got it going your way?

If good spark at all the spark plugs then it isn't the coil pack. Try swapping the #6 fuel injector to a different cylinder, see if the problem follows the fuel injector?

You got a code p0306 correct?

Do an ohms test on fuel injectors, all fuel injectors should be within 3 ohms of each other. If the reading on any fuel injector is way off compared to the others, that fuel injector is suspect.

One fuel injector spec, 11--14 ohms at 50--90 degrees F.