There's nothing there on my engine either so apparently it's not used for operational purposes in the Murano. The hole doesn't actually go into the block (...you can see that in one of the pictures you posted).Does Anybody know where this hole with 4 threads leads to and what it's for..Found this today while looking around in the engine. underneath engine cover left side (battery) better details in the first picture second picture is what I found. EDIT: found a better picture of what it is but still don't know what it's for...new pic is below
If you look around the engine/transmission you will inevitably find threaded holes with nothing going in them and usually it's because those holes are used for something in another car that uses the same engine (e.g. a bracket or optional component, etc.) or they're used purely during the manufacturing/assembly process. Since the lower intake manifold is right above that hole and the knock sensor harness crosses over it there isn't really enough space to put something there so my guess is the latter.
Nevertheless, if you find out for sure please post back.