From my way back home from the track i noticed my car started miss-firing. When i got home i removed all spark plugs & only one (cylinder 4) was black; look at picture below. I changed the spark plug for another one & it started doing the same thing. Also checked for the wires to be sending current & they are so that takes out wires and coil pack out of the equation. So my next guess is bad injector? What could it be?

Guess #1, injector not atomizing,
#2, weak or broken valve spring, most likely exhaust, if it were the intake the car would be hard to keep running,
#3 would not totally rule out the coil, under load they can present as a misfire.
Take your car to a shady area and while the engine is running, see if any arc sparking is visible around any grounds from the wire or coil in question. It's hard to see in direct sunlight.

Best way to eliminate the coil AND the wire is to swap coils/wires with the next cylinder over. If the black spark plug follows over, then either the coil or the wire or both are bad. Once that is out of the way, then consider the more serious possibilities in this order - injector, then a valve. Could also be a blown head gasket.

That's what i will also do with the injector

Yeah, flipping injectors is a little more work BC the fuel rail has to come off, or at least you can try lifting a side. That is trickier BC you could induce fuel leaks if you're not careful with the o-rings. In fact, given their age, could be creating problems....but, you have the right idea.

If this is the real #4 cylinder (second cylinder, passenger's side) then you'll need to at least pop all of the pass side injectors. If it can be done. I've only removed the entire fuel rail, so only a theory for me.

That was my thought, too. Potentially a free fix.

Yep!

Changed coil pack and wire of cylinder #4 to cylinder #2. Still have the same issue. Also car had thrown out some CEL codes before this but my guess is that this is he problem.

had samei issue and was told possibly a valve seal....haven't addressed issue yet (but I didn't have any mis-firing)

I think i found my problem. Took the valve cover off & found a broken spring!

May want to check the cam as well.

Good find, as these things do happen, seen this happen several times in our lab. Most likely, all that is needed is a new spring, and hopefully the valve did not hit the piston and bend it. Make sure the valve works freely when the spring is removed, take a compression test to make sure the valve is sealing properly.