I am trying to help out my brother in law here with his 1984 GMC 6.2 and I don't know much about gm diesels, this thing smokes black so bad it looks like it is on fire, barely produces enough power to move it's self around the yard and won't even hit one lick without plugging it in and leaving it or giving it the old gas rag (gp's disarmed of course). This thing ran flawless until a couple years ago the glow plugs quit working and all but 2 of them broke off in the heads when he tried to change them. He wound up getting them out all but 1 so he put in new glow plugs as well as the controller and relay and that worked for a little while but the threads must have gotten damaged the first time because it started shooting glow plugs out of their holes after about a month. He pulls out the engine in an effort to freshen it up while changing the heads out which included a new timing chain and all the gears, oil pump and full gasket set, used a set of heads off an 82 6.2 that ran well but had bottom end problems. Also he had the injection pump rebuilt locally and installed brand new Delphi injectors. With the help of an original shop manual he re assembled the engine and reinstall it in the truck adding a turbo and all that goes with it off a later 6.5. That's about all of the story I know and I'm struggling a bit with where to start. I have already done a compression test and checked fuel pressure, return pressure and checked the gp's for proper operation all of which check out with the service manual. It's so bad with the unburned fuel fumes I can only stand to run it for a couple of minutes at a time but it does sound normal when it's running. Any help is appreciated, I have mountains of info an experience with Ford/IH 6.9/7.3 idi engines but I have never had to do anything more than routine maintenance on the 6.2/6.5 gm diesels so any ideas are greatly appreciated. thanks!