CUAV PX4FLOW USART3 Mavlink

hello,all,
I have tested the CUAV px4flow with IIC in reference to the document ,then i have got a good performance in loiter mode without GPS.Now i want to test the px4flow with its USART3 which supports mavlink @ 115200. I have got the data output in Mission Planner with a USB-UART,but it doesn’t work in the arducopter .I have set the parameters like the following:
Set FLOW_TYPE = 5
Set SERIAL4_PROTOCOL = 1
Set SERIAL2_BAUD = 115
Set EK2_GPS_TYPE = 3.
then what should i do ,thank you very much !