1993 Mercury Villager Question: Ticking in upper engine area

My villager has about 150000, and just recently had a ticking in the upper engine, cap and rotor was burnt, just replaced but still ticks, sounds almost like a diesel. Had the problem about 1000 miles before shop found two plugs loose and plug wire loose, checked those items and were all tight, so what else could it be? Check engine light does not even come on.