I have a 6 cylinder turbocharged diesel engine that has been working
great for a year. Upon removing the head for a non-related issue, all
cylinder walls are good except for number 5 which has chunks/gouges
missing all around the top 1/4" of the cylinder wall. The chunks
don't currently effect the mating surfaces of the block to the head to
the extent that the engine will run improperly, except the thinness of
the mating surface in one area is excessive (about a dime thick).
There is no damage to the head.

Could these gouges be caused an excessively lean mixture in that one
cylinder causing detonation, and if so, could that be caused by a bad
injection pump or clogged injector?

Is the most likely cause of these gouges a broken valve that was
repaired before I took ownership of the engine, or something else?

Thanks for any help...