Some of those earlier ones have that stupid indirect injection set up where the injector and fuel gets fired in a small prechamber then on to the piston and combustion chamber. Makes them dirty, stink even worse, slow starting and noisy. They just sound lazy. A little research tells me the 97 is direct injected and uses the stupid high pressure oil pump to fire the injector. If the oil is degraded it doesn't run well or might not even start. Then, if you don't drain the oil manifold when changing injectors you can bend valves and pushrods when you try to start it. Those injectors can also leak fuel into the oil and ruin an engine. This used to be pretty common on the DTT466 engines we used to see at the truck shop.

Some of those vans had a 6.9L in them not the 7.3L.