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Discussion Starter #1 (Edited)
I have a 94.5 psd with 280k and it runs kinda rough after it warms a bit and the idle settles down. When I first crank it, it runs fairly smooth, but with a slight shake to it and a faint thump in the airbox. As it warms up and the idle lowers, it gradually runs rougher and the thump is more noticeable. It will run like this at all engine speeds under no load. I suspect a hydraulic issue, and I hope its a lifter, but with 280k on the truck I guess it could be injectors. I have had the vc's off and checked all the poppet screws, and armature clearances are right at .002. I also ohm'd out the injector harnesses from the idm and they all checked fine. Tried another idm and no change. The DMF has been replaced with a SMF kit already. I've read that a thump in the airbox indicates a valve train issue such as bent push rod, weak lifter, cracked rocker arm assembly, or bent/burnt/leaking valve, but since it seems to be more pronounced when warm, I believe it to be a lifter. It does have a metallic sound to it as well, though its kinda hard to tell being a diesel. I have not checked lube oil pressure as I don't know where to hook my gauge to or what good pressure should be. I would imagine the pump could be at its end of life.

Sorry about the long post. I just needed a sounding board to see if I'm on the right track or not. Any thoughts?
 

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Discussion Starter #2

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I would run a cylinder contribution test first. then a compression test. If its mechanical, youll find the problem cylinder.
 
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