Sounds like progress so far. I think we'll get it figured out soon.
Here's something to keep in mind: These are extremely simple engines. There are only a very small number of things that can cause one that is ALREADY running to STOP running. Even fewer possibilities than there are for an engine that won't start in the first place!
The root issue that is preventing it from starting now is probably the same one that caused it to stall originally. Therefore, some of the things that we'd normally look at for an engine that doesn't want to start, like cranking speed, glow plug system, etc, can be ignored for now while we focus our thinking on why it stalled in the first place.
There are only three fundamental things that can cause a D24/T engine that is already running to stop running:
- Loss of crank-cam-IP timing sync (stripped or jumped or broken front or rear timing belt, or slipped crankshaft timing gear due to insufficient crank pulley bolt torque, or slipped front or rear cam gears)
- Loss of fuel supply (running out of fuel, air intrusion into fuel, restricted fuel supply, loss of power to IP shutoff solenoid, or injection pump mechanical or electrical problem)
- Loss of air supply (disintegrated air filter, collapsed inlet hose, blocked exhaust, etc)
(This of course assumes the base engine is in good health and didn't stall due to locking up after running out of oil or overheating, but you confirmed those things did not happen.)
Those potential causes above are listed in order of most likely to least likely. Unfortunately by far the most common is engine timing problems. It is MOST frequently seen if a timing belt job has been done in the recent past by someone who does not have direct, firsthand experience doing it before and wants to climb the learning curve for it in hours rather than days, and/or thinks they will be the first in history to do it successfully without the necessary tools.
Sudden loss of fuel prime while already running is possible but rarely seen on a car with plenty of fuel in the tank, and the injection pumps almost never simply fail out of the blue. A fuel filter can theoretically become so badly restricted that it is able to stall an idling engine, but usually gives a great deal of warning leading up to that point in the form of gradually increasing power loss at higher RPM. There are a few other, highly unusual possible scenarios that could cause a sudden loss of fuel supply to a running engine, like disintegration of the stop solenoid plunger or collapse/failure of a fuel line, or a few others. But ruling out timing problems is probably the task you will want to address now, before combing through the fuel system for once-in-a-blue-moon type issues.
You said the recent timing belt job was done by someone who had the correct tools and knowledge. Can you specifically list the tools that the shop told you they had and used? Was it just a regular VW diesel dial indicator for the IP? Or was it the full set of highly specialized and very rare D24 engine tools including the crank locking tool and cam gear counterhold? Did they show you the tools? Was it a shop specializing in classic Volvos? Or a Volvo dealership? Or more of a general repair shop?
Using the first link ngoma
posted above (died while running, will not restart), can you first confirm the visual condition of the rear timing belt and that it turns while cranking?
If both of those check out OK visually, is the car in a location where you would be able work on the engine to locate the flywheel timing marks and confirm whether the cam and IP are in time using a detailed technical procedure, if we walk you through those steps?
And just to cover one other easy possibility for good measure: can you confirm that the dashboard glow plug light DOES light up when you first turn the key to Run, and that 12V power is also getting to the solenoid terminal on the injection pump just above where the hard pipes connect? (Electrical problem is unlikely as the cause given you said it "sputtered out" when it died, rather than suddenly and cleanly shutting off, but let's just make sure anyway since these are quick checks.)
Welcome to the forum by the way, sounds like a neat car you have and very unusual to find in North America, we would like to hear more about it once you get it running again!