There is Timing Chain Stretch that changes the Valve and Fuel Injection pump timing.

With the exception that if the Fuel Injection Pump Timing was done after the Timing Chain Stretch that would be OK.

The Stock Injectors have tiny passages in the Pintel that can get plugged solid with Carbon.

You might or might not be able to see that if you pulled one Injector and took a look at the very tip of the Injector to see if the Tiny Hole is open or not.

Also if you pull and Injector and the metal area of the Nozzle that is exposed to combustion is burned/erroded away those Nozzles have been in the Engine a long time.

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84 300D, 82 Volvo 244Gl Diesel