motor runs ok -- popping in airbox, narrowed down to #8 cylinder -- sound like anything common? camshaft maybe? its a 98 35oohd -- 90k -- i got as far as getting that valve cover off tonight -- need to dive into it tomorrow!! any help??? thanks

pull your valve covers and check your rocker arms I bet you have one broke I have seen this a few times on the 6.5 I don't think they oil real well on them and wear out.

ya i have that cover off -- all the rockers look ok and none flopping around. from the beginning, i started by pulling all 8 glow plugs to do a compression test -- 300 psi all around but i noticed the "popping" stopped with the glow plugs out so i put them back in 1 by 1... popping came back when i put #8 plug back in -- thats the one that was sooty! so i figured a busted rocker... pulled turbo etc to get valve cover off but all looks good there. i havent had anyone here to crank her over to make sure all are moving ok -- possibly bad lifter or cam lobe ya think? i dont think it would be a burnt valve with 300 psi compression do you? thanks

No I dont think you could have a burnt valve pull the rocker shaft off and look at it real close I still think that is where your problem is. I cannot remember exactly what happened to the two I had do the same thing but it was rocker related. spin your push rods and see if they are bent.

will give it a whirl monday == got tied up slaving around the house today for the misses!!!! truck is at my shop. thanks and i will post again monday night.

found problem today -- collapsed lifter for #8 exhaust valve! couldnt tell by looking but once i pulled rockers and tried pulling pushrods it was pretty obvious seeing how the pushrod was stuck in the lifter. pulled the head -- ordered parts - should be running again in a day or two! thanks for replies

Be careful with those pushrods, you don't want to put them back in upside down.

That really sounds familiar too me.