JEEP GRAND CHEROKEE SMOKING PROBLEM

Trouble shooting: Can someone please help! I have a 2004 jeep grand cherokee fitted with a 2.7 Merc engine. [150kw hi output engine]My jeep has a smoking problem. The mechanic has replaced the fuel pipes, checked the injectors [with the jeep analizer meter]and replaced injector no 2. It still smokes. He then identified the gas recirculation solonoid to be faulty and replaced it as well. It is a lot better now but it still smokes like when one stops a bowl of exessive smokes comes from the exaust.The power is fine and she idles even. When you acccelerate I was told that it is normal that the smoke [then greyish] will be excessive because of the boost of the turbo but when one cruises and exelerate normal black smoke will be seen which is clearly excessive. What can be the problem now as it seems the mechanic is also in doubt[he has 18 years experience with jeep and mercedes]?Jack