have an 86 sdl with a knock.just number 3 cyl.cracked inj lines and number 3 is the culprit.knocks pretty good up to about 1200 rpm then it's gone,i switched injectors with 2 other cyls and it's still #3.i also have a very minor rough idle.does this sound like delivery valve seals or do i need to dig deeper.one thing i noticed is if you feel the inj lines the #3 line has a distinct pulse to it where the others you can just feel a little tap.