input please

I was driving my car and at about 2500 rpms it started running like crap. I pulled plug wires to find that cylinder #3 was not firing. It is getting spark, just not firing. I want to know if you guys think its a bad injector, a cracked piston, or a stuck/bent valve. Also if you guys know of any tests that don't require a cylinder leakage tester.

What's the number 3 spark plug like??

Could be anything.
How clean is your injector......?

-Phil