why can not control gpio 88

I am using am3517 som-m2 ,I want to control gpio 88,i do as follow

cd /sys/class/gpio/
echo 88 > export
echo out > direction
cho 1 > value

but i can no get 1,always 0

but

echo 118> export
echo out > direction
cho 1 > value

i can get  1

why? anyone who could help me, many thanks!