Hi Im working on a 2003 ford f-250 super duty 5.4 liter engine reg cab 4x4 w/120k miles it wont start i bought it a few weeks ago and was driving it home about 150mile away it had a valve tapping sound alredy when i got 15 miles from my house it died it started black smoking then a major loss of power then died. it turns over fine it almost wants 2 start be wont it sounds like timming is off it pops and back fires and it has a lopping when tring 2 start any advice would be helpful ty Ron