I have a knocking 6.2 . It has been knocking for about a year now, I always thought it was an injector but I am not sure. recently the knock has gotten louder so I went to a stanadyne service shop with my truck and the whole time I was there it did not knock, but of course I got home and it was knocking again. I will try to explain the symptoms. When I start the truck when it has been sitting for a while, the knocking is not immediate as the engine starts, the knocking only apears after the engine has been running a few seconds, almost as if when pressure builds up either in the lubrication system or in the injection system. Also the knock apears to sound worse when the fast idle is on , but could just be because the engine is turning faster that it would apear that way. also it is a bit quieter once it has warmed up a bit. Anybody ever experience this? thanks.
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Do you get white smoke? Does it idle rough?
I suspect injectors right off the bat, have they ever been replaced? If they're over 100k, they're past due. The next likely possibility is valve train.

Check the flexplate to convertor bolts (loose) and bolt holes for out of roundness. Cheap and easy to do BUT the first time my 6.2 "knocked" it was injectors and I only fond them after checking the bottom end bearings with the engine still in the truck. Injector can be tested for good pressure and spray pattern by a good diesel shop