1999 F-150 knocking issues?

[fireguy]

My buddy's truck is making this strange knocking sound quite a bit, just not at idle.. There's also some black residue that comes out the exhaust. Idk if he's got some mad carbon buildup or what.. I have a video from his phone if you'd like to hear it; Idk how to post it though cuz it's from his sprint phone to my email, so I'd have to forward it to you.. Sorry if this seems real vague, any help would be greatly appreciated.

[Texas Tracer]

Is it a 4.2 v6? They had intake leak problems that would cause coolant to get in the engine and make a knocking sound and eventually f the engine. Happened to my dad's econoline but we caught it before any real damadge occured.

[fireguy]

it actually has the 5.4L