Check that injector that appears to be leaking.
Check the connection of the injector pipe on the injector. If this is not the cause then the chances are that it could be the sealing washer at the bottom of the injector in the cylinder head. This will cause a lack of compression on that cylinder. As for the blue smoke on start up that is generally oil burning ( then it clears according to your description) Check valve stem oil seals.
A compression check is worth doing for sure because if this is not within limits then all other attempted engine adjustment may be in vain.
Remember an engine is just an air compressor and if its loosing pressure it wont perform to the design specs. Compression test first.
Hope this helps