Well, I would want to mention that I a.)don't yet own one of these and b.)haven't worked on many GM diesels. So as much as I'd like to help, use lotsa common sense with any of the stuff I point ya toward. It might be the answer, or might be a wild goose chase.
Glow plugs: you can check resistance in the plug with an ohm meter, a bad one should be open (like a blown fuse). I think you can also check voltage drop at each glow plug, seems like I remember someone mentioning that in another thread. Other than that, I don't know of a reliable way to check them, without risk of damaging them. I'm sure there would be a way to connect them to a battery and see if they get hot, but 12v directly to them would be bad (I want to say they are built to operate in a 2-4 volt range each, with all 8 sharing the 24v bus).
Cams:
If your cam had 'skipped' due to a slack chain, it would throw the cam timing back (I guess) around 2-5 degrees, which might be enough to keep it from running.
Being a diesel, if you have good breathing, cam timing and compression, I think it should run with a shot of ether.
If it were a gas engine, we'd need to add a good ignition system to that to make the same statement. Diesel means we can forget about strong spark, correct ignition timing, advance, plug wire connection order, etc.
So since your engine is turning over, and does not sound like it lacks compression, then I'm wondering if something is keeping it from breathing. Is the engine giving 'puffs' out the tailpipe while cranking, and breathing in through the intake while cranking?
I suppose if the unit got into a muddy river, stalled, was pulled out, and the muffler/exhaust is full of mud then you might just have a fix there by cleaning it out.
That seems to be supported a little due to the 'kick' at first, then nothing. If the exhaust or intake are plugged, then the cylinders are full of burnt air/fuel and won't light off again. I'd try having someone crank it while I went to the back to see if air comes out the tailpipe. You ought to feel puffs on the back of your hand at least. Of course, you could also drop the exhaust at the y pipe under the engine and see if it runs with the whole system disconnected. Maybe he backed into something and bent the exhaust closed, but it was able to run enough to get home (but not start again).
In general terms, cams can jump time (usually lagging) due to wear in the gear/chain/belt system driving the cam from the crank. Gear driven cams (lawn mowers, air cooled VW engines) jumping time usually means a broken tooth in the system. Chain driven cams (your case) would be due to a broken tooth, weak chain, etc. Belt is usually a lucky break, giving warning before the belt snaps. Most timing belts just fail, and it seems like I hear more about the cam drive system failing rather than 'jumping time'. On an interference engine, that means valves kiss pistons goodbye.
I'm assuming that your diesel's cam drive looks a whole lot like a standard gas V-6/V-8 system (different actual parts of course). Small sprocket on the crank, larger sprocket on the cam, and a very short chain (enough of a loop to allow the two sprockets to not collide, but not much more) connecting them together. All of this is under an oval shaped cover behind the water pump on the front of the block. A friend of mine and I replaced one of these sets on his Dodge 3.9L V-6 (which is basically a Dodge 318 with two cylinders cut off). There are curved metal 'tensioners' that the chain rubs against, which keep the chain from flapping around in service. After replacement of the cam sprockets, tensioners and chain, his engine had a noticeable improvement in power (more like restoration of factory power). Slack in the chain will allow the cam timing to drift farther after-top-dead-center, and since his distributor was locked to the cam, the ignition base timing was lagging time as well. The new chain brought both back to factory specs, but his engine had over 150k miles on it, so his old chain was quite worn.
Checking the cam timing should be possible by pulling the valve cover(s) and seeing when the valves open / close as the engine is rotated by hand (with the glow plugs all removed). There should be a spec somewhere saying what the timing and the duration should be for the cams (see when the rocker arms move relative to the crank position in degrees).
Of course, pulling the water pump and cam cover will tell the story right away but I'd rather not suggest jumping right to that.
If you have another (running) GM Diesel engine of the same spec as the non-runner. you could pull the left valve cover on both and see if the #1 rocker arms start moving at the same crank degree point on both motors.
First I think I'd look for obstructions in the intake/exhaust to make sure it's getting air through it. I would not rotate a diesel by hand unless I was sure it could not start (glow plugs or injectors pulled to prevent compression), plus I think it may be unrealistic for a person to be able to rotate a diesel by hand without a compression release of some kind.
Hope you find the problem!
