gistfile1.txt

This code is here to be accessible to anyone trying to solve this issue on StackOverflow http://stackoverflow.com/q/37789605/955143

Input

FD1	FD2	FD3	FD4
--	--	--	--
2	3	3	5
AACCC  FUUUUU
AAHHH  FGGGGG
55HHH  FVVVVV
55HHH--LVVVVV
PPNNN  LVVVVV
PPJJJ--LDDDDD

My code, copy/past into a new module in excel

Sub LoopParser()
	Const SizesRow = 3
	Const DataStart = "A4"
	
	Dim ToCut
	ToCut = 0
	
	Range(DataStart).Select
	
	Do Until IsEmpty(ActiveCell)
		ToCut = ActiveSheet.Cells(SizesRow, ActiveCell.Column).Value
		
		Call ParseOneField(ActiveCell.Address, CInt(ToCut))
		ActiveCell.Offset(0, 1).Select
	Loop
	
	Range(DataStart).Select

End Sub

Sub ParseOneField(TargetCell, DesiredSize As Integer)
	Const MaxLayout = 10000#
	
	Range(TargetCell).Select
	Range(Selection, Selection.End(xlDown)).Select
	Selection.TextToColumns _
		Destination:=Range(TargetCell), _
		DataType:=xlFixedWidth, _
		FieldInfo:=Array(Array(0, xlTextFormat), _
						 Array(DesiredSize, xlTextFormat), _
						 Array(MaxLayout, xlTextFormat) _
						 ), _
		TrailingMinusNumbers:=True

End Sub


FD1	FD2	FD3	FD4
--	--	--	--
2	3	3	5
AA	CCC	FUU	UUU
AA	HHH	FGG	GGG
55	HHH	FVV	VVV
55	HHH	--L	VVVVV
PP	NNN	LVV	VVV
PP	JJJ	--L	DDDDD

When the expected result would be (preserving blanks in the third field)

FD1	FD2	FD3	FD4
--	--	--	--
2	3	3	5
AA	CCC	  F UUUUU
AA	HHH	  F GGGGG
55	HHH	  F VVVVV
55	HHH	--L	VVVVV
PP	NNN	  L VVVVV
PP	JJJ	--L	DDDDD