you'll need the serial number of the engine, the complete engine model number and possibly a CAT number and/or any other info you can get off the engine data plate. What type of equipment it is in etc.
If the engine is in a certain type of equipment you won't get much help from the machine mfg. you'll have to find a Deutz engine dealer if your looking for engine parts related to fuel or any other internal parts. All you'll get from the equipment dealer is probably just filters, belts stuff like that.

What is this engine in?