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If the engine has external fuel lines going to injectors inboard of the valve covers (on the intake manifold side on the cylinder head) and you can see the wires going to the glow plugs in the same area of the head, you have the IDI engine. If your engine wiring harness snaps onto a pair of connectors on each valve cover gasket you have the Power Stroke. In 1994 most of the vehicles equipped with manual transmissions had the Power Stroke (except very early in the run) and most of the automatics had the IDI engine (except very late built vehicles). If your fuel filter is an external cartrage type, you have the IDI. If it is an element inside a filter housing, it is the Power stroke.
There is probably some character in the VIN number that differentiates one from the other but I don't know the code. Maybe someone knows what each letter stands for and can post it here.
OK, here's another: If you have a throttle linkage going from the fire wall to an injection pump you have the IDI. If there is no throttle linkage you have the Power Stroke.