The best Diesel Engine troubleshooting advice I ever got, and that I will now pass on is:
"Diesel Injectors are guilty until proven innocent."
So far on this 500K Detroit Diesel 6-71, I've pulled the cover, Jake Brakes, and all six injectors. I dropped them off at a local place, Diamond Diesel and Turbo here in Oakland, for a pop test and eval. $30 later, and I've found the most likely cause of my one-cylinder misfire:
Injector #4, Stuck Open
The injectors on my Detroit are "unit injector" type. That is, there is no high pressure injector pump like most of you non-Detroit folks have. (I actually have never seen this set up before and can't think of another example). Here, low pressure diesel is supplied to the injectors. A check valve closes, the rocker arm pushes down, and the large volume of diesel is forced into a much smaller space, increasing it's pressure dramatically (something like 400psi, I think, without looking at the book) until the plunger reaches the bottom of the injector and the needle valve opens, spraying an atomized, high pressure mist of diesel through a pin-sized hole and into a hot and waiting high pressure cylinder, where it explodes and makes a cool rumbbly diesel noise and sometimes helps move the bus forward. Of course, if your cylinder #4 and think you can just open your needle valve whenever, you're just gonna dribble some lo pressure diesel into the cylinder and just make a smokey mess and cause a misfire. No high pressure, no explosion, engine no work.
So anyway. 95% chance I found the problem. I ordered a new injector, $50 shipped. Should be here thursday. Then I just have to put it all back together and completely redo the timing.
I'm still going to try and do the compression and leak down since I have all the injectors out... if I can source the f_____ing adapter. Most diesels, you thread the compression tester into the glow plug hole. Detroits have no glow plugs, so you have to do the test through the injector hole, and therefore have to source a "blank" injector adapter... for an engine that hasn't been made for 30 years... ugg.
All the seats are out, and I've been playing with floor plans by using masking tape on the floor.
Also, stripping the seats for the scrapper. Super unrewarding with scrap prices low like this. I know I'm not gonna get anything for them, but I have to do something with them.
Beer and sledgehammers are my preferred tools, but it's still kind of a drag.
I also pulled the "light channel" raceway aluminum extrusion down.
My plan is to use this as a raceway for the new 12v stuff I'm going to put in.
As an ex- east coaster who has spent some time in Florida, I was really hoping that this dry California air would mean no moldy insulation to deal with.
I trashed that stuff behind the light channel... but I'll tell you right now that I'm not drilling out the approximately 12 million rivets that hold up the ceiling panels to replace the insulation up there. If it was screwed together, maybe. But these 50 million rivets? Life is too short. I'm thinking that I'll great stuff above he channel to "sort of" seal the no-doubt gross fiberglass "up there."