Sparkfun Artemis Open log - on board IMU sensors non responsive

Thanks, just got two new boards which I updated to firmware 1.6 and IMU function ok on both boards, but am bit confused with the logging rate, in the hookup guide it mentions it can operate at a 250Hz rate, only have the IMU enabled, the serial and analogue logging are both disabled but can’t set the unit to log IMU data at 250Hz rate, any advice appreciated.