I recently purchased a 2000 Ram 2500 pickup having 79,000 miles on it in very clean condition. It was sitting for a long time and the engine was running rich and missing. The check engine light was not on and no codes were present. I decided to change the spark plugs. The plugs looked like it was running very rich towards the front of the engine on both banks. Number 4 spark plug was totally dark. I changed the spark plugs and it made a small difference. The engine was still running rich from the tail pipe, and no improvement on the missing. I pulled out number 4 spark plug and it was oily and not firing. I then decided to do a compression test. Number 4 was about 25 lbs and the others around 100. Then I decided to used compressed air with the tester hose and the intake valve on number 4 was not opening. I then pulled the upper intake manifold to pull the valve cover on the right side. On number 4 the pushrods and rocker arms are not worn or bent. I then took off the rocker arms and left the pushrods in and spun the engine. Holding down on the intake pushrod there is no up down movement coming from the camshaft. I also noticed that on number 2 the intake valve is barely opening but 6, 8, and 10 are okay. My question is this. What do I do next? I have rebuilt hundreds of car and truck engines and have never found a roller camshaft to go flat. Is there a possibility that the lifters are worn and have some kind of mechanical stop so the pushrods do not fall off? I need your help and this will be a good post to help others as well!