I have been in the slow process of replacing injectors lately. I have had a nailing problem with the #6 injector. I replaced it and the nailing went away. Two weeks ago the nailing came back and the car runs rough at start up. I have used a stethascope and know the nailing is coming from the injector. I replaced it last week and it still nails. Could this have to do with the timing?

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Owen

87 300TD 603 I-6
94 Jeep XJ I-6 4.0 (see the pattern)
89 750il
seventy-two hundred feet above sea level (kinda cold up here)