my Cherokee currently misfires in cylinder 6 but not all the time, and I can be driving down the road fine then it will start to misfire and do it for a while then it will make a loud pop sound along with a little thump the red check gauges light pops up and then the check engine light and the red check gauge light goes away. And it runs normal until it does it again. When it happens the oil pressure drops to zero the. Goes right back up to normal. Any clues on what could it be? I have checked injectors, spark, did a compression check while back,