PX4 sitl fake gps

hi ,
i modify Fake_gps.cpp to read latitude and longitude and other gps data from serial port receive data from my program to simulate gps data, then i remove gps plugin from SDF file of gazebo , however at the end when i run px4 sitl plane with gazebo , QGroundcontrol doesnt allow to arm and give me the Preflight: GPS Horizontal Pos Error too high. thanks