If the battery and starter is cranking the engine over, the engine needs fuel, compression and spark to run. More info would help us help you.
vapor lock
Timing needs adjustment is the most likely cause.
Your question is sort of backwards, perhaps you meant what causes engine failure? Engine failure causes...the engine to fail. If someone told me their engine failed I would take it to mean that it stopped running, or wouldn't start.
Check the timing belt.
A. No fuel B. No spark
Check the battery and the connections to the engine.
It's lean. You have to figure out why.
You probably have a little oil seeping into the combustion chamber while the engine is off. Once you start the engine, this oil is burned and causes the smoke you see.
There is no such engine as a Cummins 2500 Diesel.
If your engine backfires when trying to start and the valve timing is correct, then it could be electronic ignition unit or the pick up that causes the spark to occur with wrong timing.
The timing of the engine is off or the spark plug wires have been hooked up incorrectly.
there is no primer, but the 6.0 has problems with o rings and injectors malfunctioning, which causes then to not sart also check engine oil level. if insufficient oil the engine will not start