Is the engine same on a 2000 Ford Ranger as it is 2004 Ranger?

No, the engines weren't necessarily the same across all trims of a 2000 and 2004 Ford Ranger. While some engines may have carried over, there were changes and updates to the engine lineup between those model years. You'd need to specify the exact engine code (found on the engine itself) for each truck to know for certain if they were identical.