There were no turbo diesel vans before 1995, so it's definitely not a turbo.
Vapor lock? Are you sure? I have never heard of a diesel having vapor lock. Diesel just doesn't vaporize due to heat like gasoline does. I am thinking more likely that you have an air leak in the fuel system. Those fuel return lines on the fuel injectors have a bunch of rubber hoses, o-rings, and plastic parts that could use replacing. More than that, the hard fuel lines have rubber washers in their fittings that tend to break down over time.
There is a kit you can buy at Orielly's or Auto Zone that has all the plastic parts, o-rings, fuel line, and clamps (called an injector install kit for ~$60) that will solve most problems. The kit also comes with new copper washers to install new fuel injectors too, but you don't really need that part of the kit. The hard fuel lines might need new washers that may be available from a local diesel shop, or the parts stores.