Q: Misfire in number 4 cylinder

Hello. Check to see if the code defines a "circuit" that is a wiring issue with No. 4. If it does, you have to look at the signal to the injector.

Using a mechanic’s stethoscope, it is easy to hear the characteristic clicking noise that should be present if you probe the injector body and compare the noise (if present) to that from adjacent known good injectors to see if your No. 4 is even operating. If not operating at all, check resistance across the two injector solenoid terminals and compare to FSM. Depending on the code, it is that possible there is a related "ignition" issue in that cylinder, too. Particularly since you are describing the symptom as a "miss."

If it is ignition-related, you could have a bad plug or plug wire for No. 4. If you replaced it with a "used" injector, by the way, it could easily be plugged. Injectors typically have replaceable internal filters and used ones should be cleaned ultrasonically on a professional cleaning machine. It is very economical, too. Typically around $17 each at the shops which are known to do exemplary work of this type. If you would like to have this looked at more thoroughly, a qualified technician from YourMechanic can come to your car’s location to inspect the code and perform any required repairs.