the PSD is Direct Injection

The Injectors are controlled electronically and powered by high pressure oil that injects fuel under very high preassure. The high preassure oil is routed thru rails in the cylinder heads.

The earlier (pre 1994.5) diesels (turbo or nonturbo) are Indirect Injection, the injectors are mechanically operated and Injection preassure is accomplished by preassurizing the fuel with a rotary pump.

Check out this thread these guys know a lot more about it than I do.

https://www.ford-trucks.com/forums/5...?highlight=idi