Re: 2001 wj 4.7 sounds like its backfiring into the intake
Welcome to the garage.
If a rocker fell off, you will get a misfire and normally it will show a P030X, where the X is the cylinder number. Did you check for any fault code set doing the keydance? Ignition switch off/run three times and leave it in run at the third time. The odometer will show Done when all ok, or any fault code(s).
If there was a big air pocket stuck somewhere in the cooling system, the engine will get very hot at that spot, while the coolant temperature indicator can still show a reasonable temperature. If this engine overheats, it can warp the cylinder head(s) and a valve seat can get loose and drop. This last will cause the respective rocker arm to fall of and can cause severe piston and combustion chamber damage.
But first look for any fault code and let us know.