with mach 3 according to manual  i use the following program to check the step error
F1000 (i.e. faster than possible but Mach3 will limit speed)
G20 G90 (Inch and Absolute)
M98 P1234 L50 (run subroutine 50 times)
M30 (stop)
O1234
G1 X4
G1 X0 (do a feed rate move and move back)
M99 (return)
but after finishing it i found it not go back to the same start position
can u help me to solve this problem

How much is it out? Do you have any backlash? If you have backlash comp switched on is it set correctly? Could you be missing steps by having your motors tuned to aggressively?

Hood

it's about 0.4%  and i haven't backlash 
how can i know if i missing steps

You can usually hear if they are missing badly but if its just the occasional then you may not. Try increasing the pulse width to 5 and see if that helps, you could also try changing the active state  for Step and Dir pins.
Hood

i already increased the puls width to 5 for pulse width but not for direction puls
now i choose active low i'll try to use active high then i'll inform you

dear friends
i start today to test the machine but i'm very surpriues because when i change the feed rate i found the distance also change acoording to feed rate vatue can anyone help me
thanks

Please attach your xml.
Hood

this xml
F1000 (i.e. faster than possible but Mach3 will limit speed)
G20 G90 (Inch and Absolute)
M98 P1234 L10 (run subroutine 50 times)
M30 (stop)
O1234
G4 P02
G1 Y40
G4 P02
G1 X40
G4 P02
G1 Y-40
G4 P02
G1 X0 (do a feed rate move and move back)
M99 (return)
%

No the xml is your configuration file. If you are using the standard mill profile then go to the Mach3 folder and look for Mach3Mill.xml, copy it to your desktop and rename it osman.xml
On the reply page you will see additional options, use that to browse to your desktop and choose the renamed file.
Hood

dear hood this is the last xml ido yasterday