what are the common problems on a 4.6 v8 ford motor

main and rod bearing rattle. l have a 99 f150 with 140,000miles that rattles when l start it up. quiets when oil pressure comes up. l plan to rebuild soon.

too small of bore. too short of a stroke. those are the 2 biggest problems that engine has.

only real problem seen a lot is spark plugs blowing out of the heads

-Split plastic intakes in the water passage directly behind the alternator that leaked antifreeze. The later models were updated with an aluminum passage integrated into the plastic intake.
-Spark plug Coil is start going out after 75k & there is 8 of them.
-Spark plugs blow out of the hole taking the threads with them. BTW, Yes 'david z' I've seen the 4.6 do it too. As recently as 2 days ago in an expedition.

l own an '01 Town Car with 98k & quite honestly expect it to run forever. Despite any common problems, these things do not stop.
2 things that MUST be done is to use only Motorcraft oil filters. They have a drain back valve that keeps oil from draining back to the pan when the engine is off. Most aftermarket filters do not. This prevents knocking on start up & eventual damage from it.
Use only 5w20 weight oil if that is what it call is for. The tolerances r very tight in the valvetrain & any heavier of an oil can eventually cause valvetrain problems because the hydraulic components stay pumped up & never bleed down like they should when the engine is running.