obd2 connector help

[lilrobo]

guys i have a 55 with a 5.3 from a 06 truck and computer from 02 camero ,, all has been great , i have loaded tunes and played with it tons ,, i did a push button start and now i cant load a tune, it says cant connect and to check connection ,, i can scan and do log runs , so i think i am linking up to ecm ??
i have 4 wires
purple = data
black = ground = chassis
blk/wht = ground = signal
orange = battery
the ground check out i check with ohms all good , the orange is 12 volts hot all the time ,, how do i check the data port ? i dont understand nothing changes when i go in to acc mode . or what is suppose to happen that mode

thanks