02 Dodge Dakota 4.7 did the same thing at first it was running fine had a little tap in the engine I noticed pulled the valve cover to rock arms are off slip new ones back on started it back up started running rougher and s*** loading up flooding out real bad started backfiring through the intake blew the top of the intake the back of the intake off change the intake got it all put back together new injectors new plugs same coils and tried to start it wouldn't start wouldn't start wouldn't start wouldn't start kept on kept on kept on with it finally started run rougher and crap would not idle switched it off let it set started it back up all the sudden sound like a bomb went off blue half the right side valve cover completely out of the truck in pieces half the valve cover is still there the other half is gone explosion not sure why loading up I unplugged you injectors I had a code for a p 0201 and 0207 and that was the injector one and the injector 7 unplugged those started it back up and that's when the valve cover exploded not sure but had been starting to backfire through the engine to the intake and no more straight idle either I had to wrap it up wide open or hold it at the Thousand RPM but it would not idle at all by itself changed injectors still throw the code for the injector not sure why I changed crankshaft sensor changed out of position sensor change the throttle position sensor change the map sensor change the Ambient Air Temperature Sensor change the O2 sensor drilled a hole through the cat everything and it's still blue the left side valve cover completely halfway off completely off half of it completely off not sure truck runs fine up until it started not running fine $240 some miles not a minute's trouble ever great little truck four-door four wheel drive short bed love it not don't understand what happened to that never seen one blow a valve cover completely apart aluminum valve cover completely apart blue it out of the damn truck crazy

 

Well here is my hypothesis for what it's worth (not much).

You know that cold start tapping that usually goes away once the engine is warmed up? Well that is usually caused by worn hydraulic lifters that bleed out oil while sitting, then take a long time to prime. Once primed, they become hard vs springy and now you have proper valve clearance and the tapping goes away. Well, if you let those bad lifters stay in long enough, eventually one seizes and they can no longer keep tension on the rocker and so it ejects. Sometimes the ejected rocker comes to rest in a position that does no harm. In those cases you will get a misfire of the cylinder from where they originated. Other times, they get caught up in the machinery and then the carnage you described ensues.