I had a misfire on 1 of 4 cylinders due to a clogged injector in my Mazda. It was clogged so bad that it was not ionizing the fuel properly, thus the cylinder was not firing. I ended up pulling all of them out and spraying them inside and out with carb cleaner. Fixed the problem immediately and the car even feels like it runs smoother/has more power after this. I put the clogged injector into a different cylinder just in case it wasn't the problem (or if cleaning them didn't work), but it turns out that they just needed to be zapped with carb cleaner. You can also test the resistance with a multimeter and obviously the impedance should be the same in all of them. If one of them is off, it's probably bad. Also you can put a blade screwdriver to the metal part of the injectors and the handle to your ear, and listen for the "ticking" sound they make when firing, they should all sound the same. And don't forget to lubricate the o-rings and such before reinstalling the injectors, taking care not to get any oil into either of the ends.