my E 320 have a misfire code p300 and p305 andp306

I have check fuse near computerfive fuse plus a large fuse all good i just want to know mercedes scan tool can or should detect a bad computer because the technician say the computer is good but when i disconnect the fuel injector connector and plug in the noide light in # 1 it did not light up when i start the car is tell you that the computer is bad i do know tell me.? no modifications have made to intake or exhaust.