I've had an engine knock for awhile, and I'm finally going to have the time and money to fix it. I know the source is the #6 cylinder because the sound goes away after you crack the injector line. After lots of research, I've seen three likely causes: 1)rod bearing or wrist pin 2)piston slap and 3)bad injector. I'm assuming that with the miles I've put on the truck, a bad rod bearing or wrist pin would have failed long ago. Any further insight or advice would be appreciated.

 

what year is it ?
a bad inector may cause a miss , but should not make a mechanical knock sound ...

 

It's a 99 4x4