1997 Chevy Truck ECM orb ii comes up "no link"

i have tried several scanners , even stores rental , still says theres no link , took to a repair shop , they did a connections test and basic overview stuff , they had same thing no link , will the truckeven run if computer is fryied it still runs ok cokes and lungs abit when cokd and does fine warmed up , can you shed any light on this as to how to fix
thanks
Perry
ps .1997 chevy stepside short bed xcab with 5 speed manual trans ,5.7 v8 , motor was recently replaced and basic code search reset