Does anyone know what could cause the engine to so loud? on 2001 Ford Expedition

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I have a 2001 ford expedition 5.4 4x4 eddie bauer edition and was driving down the road heard a loud pop and the the truck sounded like a pulp wood truck going down the road. what could this be? the engine light blinked and then went off. is driveable but is very loud coming from the engine and it will not stay start. no oil is leaking and drove it home from work.
(1) Answer
sounds like you blew out a sparkplug. with engine running, look at top of engine beside valve covers. if plug blew out will have coil popping up or completely popped out of plug hole. will have to have helicoil installed if it has.