#3 cylinder misfire
 

my 2008 Ford Ranger 3.0 has a #3 cylinder misfire, when i bought the truck i was getting P0303 code for a misfire, i replaced the spark plugs and then swapped fuel injectors to see if it would follow to another cylinder, the code hasn't come back yet but the misfire is still present, when you unplug the injector nothing changes, if i hold a screwdriver to the injector you can hear it clicking but its hard to tell if im getting the sounds from nearby injectors without a stethescope, can anyone give me some advice

Do a compression test
Cold engine, remove all 6 spark plugs first
Test each cylinder and write it down

After changing a spark plug and still having a misfire you are then wasting time and money unless you do a compression test