87' 740 turbo - no power on boost

[mitster]

Hey guys, been trying to solve this on going problem with my sisters car.. it starts and idles fine and drives fine until the turbo spools and gets past atmospheric.. at this point the acceleration gets worse even though you can clearly hear the turbo blowin (gauge well into the yellow).. checked the ground connections on the head and intake, seemed good, replaced tps, replaced knock sensor, replaced hall sensor, tried another ecu, checked cam timing, and now im out of ideas... had a volvo mechanic friend lookin at it prior to my fiddlin with it and he seemed to think the ignition timing was retarded too much.. but ive done everything i can think of to tackle that problem... anyone else had this happen?? any help greatly appreciated, thanks.