Soaring profits among Japanese manufacturers are masking weakness in exports as the yen's slide against the dollar fails to deliver the boost seen after previous bouts of currency depreciation.

Export volumes fell 1.5 percent in 2013 from the previous year, Finance Ministry data show, even following a 12 percent decline in the yen against the dollar during 2012. That contrasts with a 7.8 percent surge in 2006 after a similar currency move.

The loss of competitiveness reflects yen strength from the 2007 onset of the global credit crunch until Prime Minister Shinzo Abe started a reflation campaign in late 2012, a period when capital spending slid 37 percent.