C-15 6NZ fuel knock??

I have a knock in number 6 that is driving me bonkers!! The knock started a few months back and was out of the blue while bob tailing to town to pickup a load. Knock got a lot worse once I had a load on and really loud in a pull so I dropped the load and headed for the shop and now after bearings, oil pump, rebuilding head (had 4 intake valves an seats beat out), new updated transfer pump, big fuel line kit (reversed flow thru head) and 3 different injectors in #6 the knock still persists. Recently the fuel pressure has started fluttering with the knock. I'm assuming this is a blown injector o-ring. It had liners put in a couple of years ago and they still looked like new so I didn't see any reason to pull the pistons as it doesn't burn any oil. The pistons were reused when liners were changed. I've had a few people say it could be a broken piece in the skirt that hasn't broke clear out. Wondering if I really screwed up by not pulling them since I was there... Just wanting to rule out everything else before pulling the lid off again. The knock gets worse in colder temperatures and does it at idle and all the way up. The computer and wiring are all original and spent its life mostly in colder temps so I was wanting to change them for good measure anyways but hate to spend the money there and then lose a piston. Trying to decide which direction to go in figuring this thing out. Any help would be greatly appreciated!! Thanks in advance

 

I was thinking the same thing at first, but after running the rack numerous times and even swapped rocker arm assemblies around just to make sure I wasn't missing something I've ruled that out and I miss spoke I've actually had 4 different injectors in that hole as I swapped them around the first time it happened tryin to eliminate possibilities. Thanks for the input!

 

Yep, all rpm's and worse with a load and worse in the cold. The best way I can describe the sound is a cross between an exhaust leak and cold piston slap and starving for fuel. Sounds a lot like the isx's do when you start them cold. It seems to be when the injector hits that it knocks, of course it gets kind of hard to keep up with over an idle but seems like it stays with the injector. That's why I can't help but wonder if its not in the wiring or computer. We had another cat burn up one hole 3 times before figuring out it was a computer that was over fueling that hole. I keep checking the temps at the manifold and it isn't running hot.

 

No problem, thanks for the help. Just did bearings on it and checked the wrist pins again while we were there everything looks good. There was only one bad valve on four different holes. The intake valve on the intake side of the motor on everyone that was bad. Machine shop said that seemed weird and contributed it to the cold air in the winter takin a toll on a hot valve. With temps as low as -50 to -70 in the winter up here I could see that being a possibility. The exhaust valves were all good.

 

Yep, that's what I was meaning. Sorry should've described it better, when we changed rod bearing we checked everything out while the rods were loose. Everything looked and felt good.