motor knock at high speeds.

[busyizzy]

So i have searched for a similar problem to no avail. the truck started knocking at high speeds about a month ago. talked to some people, and ran a contribution test. had a cyl 3 fail, but no other codes being thrown. went and got a full set of injectors and glow plugs put in, all went good until i did a contribution test. cyl 3 still bad, and now its throwing cyl 1 and cyl 8 faults. buzz test passes and the truck has no other codes, but now every time i have been on the highway for more then 20 mins at about 1800 rpm or more i get a really bad knock like a car valve tick but a little less metallic. stops when I'm off the throttle and stops when I'm off the highway no matter the rpm. check and all the injectors are seated and the under valve cover harnesses looked ok. dont know where to go from hear. don't want to just start replacing things i dont need. its a 99.5 f350 6 speed.

[jc82chevyman]

Check your HPOP level, after it happens and see where the level is at and check your IPR, ICP and your IDM you are going to need a good scanner like AE the check this stuff but thats where I would start