I am not sure what time of fuel injection pump you have. If it is a separate fuel injection pump that is lubricated from the engine oil people have said if the little O-ring in the Fuel Supply/Lift Pump goes it sucks oil out off the Fuel Injection Pump and it ends up burned as fuel.

Valve Guides and or valve stem seals.

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84 300D, 82 Volvo 244Gl Diesel