She's got the jitters, captain
 

Hello all. I have noticed a rough idle and a mild skip, lately that appears to show up after the engine warms up. Tailpipe smoke usually accompanies this - bluish. The fuel and air filters were replaced recently. I did a Diesel Purge at that time, too.

So, I set out to perform my annual valve adjustment and found all the exhaust valves tight and a few of the intake valves passable, but I loosened them up a little, anyway. I noticed no change in the rough idle/skip.

Then, I continued in the diag process and loosened each of the injector lines - one at a time- to see if I could isolate the alleged cylinder. The engine responded to each of the injectors being loosened, so I wondered if injector balance could be the issue. I decided to perform a compression test while the injectors were out and found 420psi -across the board- on a warm engine.

I put a set of used injectors from a spare engine in (not rebuilt or pop tested) and started the engine. The smoke is gone, but the rough-idle- while-hot issue still exists.

I feel like I have accomplished a lot of maintenance tasks today, but I have not resolved the original concern. I am happy to see those compression numbers.

Sooo...is my concern actually related to a rack dampener problem? Can a rack dampener cause a pseudo rough idle/near skipping hot idle concern? It smooths out above a 750 rpm idle. OR Is it an IP element/IP timing symptom?

Mark,
I dont know about the damper, but it is unlikely that its an IP timing problem. Element or DV is a possibility but its strange that it isnt just one. A check of the damper is probably a good idea. whats the timing chain tensioner like?

Yes.

Adjust or replace the rack damper bolt.

Timing chain and tensioner is original. I did the rough, inaccurate way of checking. It has 5 degrees of play in it, and will need to be replaced soon, so there is a difference in injector timing, I'm sure. i will check the damper and go from there.

My understanding is that the 85's had a different design rack damper from earlier year models, right? Can they be adjusted? or Do you replace only?

Ok. I just adjusted the rack damper and it has gone away ... for now. I will drive it and see how it does over night.