Hi friends.
The problem is already solved.
I used two diferent sources. One for Arduino and one for the sensor y load.
With this configuration forced me to join the GND, and here was the problem. Now the Arduino and the sensor use an external source and load another.
The measurements are correct:
Load 1A= 23mv.
Load 3.20 A = 67mv
Load 4.20 A = 90MV.
Thank you both.