3406E vibration and very slight mis at higher rpm

Maybe some of you cat guys can help me out... here is the story. Family member just bought a 2000 classic with a 2WS cat 3406E. Has 820k miles. Truck was serviced and takin care of regularly, coolant system is clean and internals clean. It was traded in because previous owner thought engine needed rebuild. We pulled valve covers after getting it and found a roken #4 injector spring. I replaced the #4 injector with new cat injector and did a fine tuned overhead adj. On it and changed trim code. Truck runs much better now and has power back but still noticing a vibration (ruled clutch out) and when running rpm up at 1400-1500 rpm there are a few slight hickups. Could this be from a bad injector harness? (13yrs old) i checked over the fuel system and changed filters. Also performed cutout test and keeps saying #2 fails and to check connections on injector. Which i did and nuts are tight. It runs good otherwise, no smoke at all and nothing has been touched besides overheads, still paint on all engine bolts. Is it common for these to have a dampner create a bad vibration thru cab?

 

Thanks, I will try the injector harness first. Are injector harness problems somewhat common on the 3406E? I know the detroit 60 engines had some problems with oil wicking and ive done those before. Just curious if this is a rare occurrence?

 

Well after replacing the injector harness and changing out another bad injector i got the engine running correctly. Now i need to figure out what is up with this vibration... it starts at about 1100rpm up to1500 rpm. Engine sounds smooth and no smoke or anything odd. The clutch was replaced a few months ago. Engine mounts are old but seem ok yet. Should i try a new dampener? It idles very smooth also.

 

Yes i did try pushing clutch in with truck sitting still idling also and no change. Its a real mirror shaker at 1350the rpm. I picked up a balancer so i will try that next. It seems to be running healthy and has good power so i wouldnt think it would be an internal problem would it? It has a dyno run scheduled today also so maybe that will help figure something out.

 

Truck ran great on the dyno. Rated 500hp. It ran 415 to the ground and blowby was 0.9 peterbilt guys said he would look into the clutch making the vibration. Is it possible to pull the clutch/flywheel and have it balanced together someplace? If i need to.