Spark goes away in one cylinder

Have spark failure on number two cylinder. Have changed the coil and plug on it. Runs fine for a minute then starts missing again. Pull coil and plug and check it plug is wet with fuel. Check for spark and nothing. Put a different coil (old one) on it check for spark. Pretty blue and consistent. Change back to new one and again check for spark, pretty blue and consistent. Reinstall both and fire it up. Runs good for a minute then back to badly. Pull both again and check spark. Nothing. Go through same procedure as above and spark comes back again. Would cause this? Also no codes being thrown. Have also changed injector and checked both with ohm meter perfect 12.5 as also with all other five cylinders. All 12.5 ohms. Input is exactly the same on all six even when misfiring. Anybody have a clue?