not sure if this helps but maybe an exhaust leak before the turbo (i.e -cracked manifold, bad exhaust mani. gasket) could be a possible reason why your not boosting. i experienced a similar problem and couldnt figure out what it was until i pulled the maniold and saw a large crack,the gasket had deteriorated and 6 out of 8 studs had no threads to bolt on too. car was definately a COW because of this. Hope this helps