Tom,
Are you making your software clear the CCF4 bit each time you get the PCA interrupt? If not then the MCU will get interrupted over and over until such time that this bit actually does get cleared.

Note that if you do start to use the PCA overflow then at each overflow interrupt you must also clear the CF bit.

It is a good idea to structure the PCA interrupt service routine in such a way so that it has code that looks similar to:

      IF CF Flag Set Then
           Clear CF Flag
           Do other Overflow work
      ENDIF

      IF CCF4 Flag Set Then
           Clear CCF4 Flag
           Do work associated with the capture function
      ENDIF

Michael Karas