I have an 85 6.9 diesel. A couple of months ago I noticed that a slight clacking or ticking noise had begun to develop. Along with this I noticed that, at times, I would get a little blue smoke rolling past the window while at stop lights. Accompanying this blue smoke would be a bit of a rough idle. About a month into this issue a fuel station accidentally topped my tanks off with gas. I drove it for about a half hour before figuring out what had happened. had the tanks removed, cleaned, fuel filter and water separator replaced, etc. After this, the blue smoke and rough idle seemed a little worse, with the exception of when I first fire it up in the morning. When I fire it up, it runs smooth, and Im assuming this is the case due to the cold idle assist. After the cold idle disengages, it idles rough. Yesterday I was coming down a long steep grade and noticed that after rolling down the hill with my foot off the the throttle, and then pushing down about a quarter throttle to maintain speed, a lot of blue smoke would boil out the tail pipe. This continued all the way down the hill. If I mashed the peddle or just maintained about half throttle while descending, the smoke would clear up. Going up hill, the smoke would go away. For the record, the engine doesn't leak oil at all. I replaced the fuel injection pump about a year and a half ago. The oil always looks exceptionally clean in this thing --compared to another one I owned, and diesels in general. So I was wondering what others might have to say about this problem. It currently has Stanadyne injectors in it, and I don't know if this is an actual date, but they have 11-90 stamped on them. Also, a couple of the injectors (two of them) were leaking after the gas incident. It was puffing blue smoke a hell of a lot worse, along with a rough idle, at that time. I replaced the O-rings on those 2 injectors and the leaks stopped and the idle smoothed out a bit, along with the excess blue smoke. But it didn't clear it up entirely. Anyway, this a long description, but It might help narrow down some potential issues hopefully.

Thanks gentleman,

Jeremy