poor running

Help! my swb ducato 11 has developed a running fault. Originally associated with the EGR valve, now replaced it is low on power going up hills and pulling away. We took the vehicle back to the main dealers, they suggested turbo or fuel pump as being faulty. Disputing this the vehicle was taken away from the main dealer to a diesel specialist they found an air leak between manifold and turbo. This leak has been sealed but the engine running is far worse than when it went in for repair. It will tick over but when revved pours out black smoke of huge quantities. The specialist suggests the air mass sensor, now on order and advises us to change the full exhaust system because they suspect either a blocked catalist or possible exhaust pipe obstruction. The fuel pump and turbo have been eliminated, so has the new EGR valve, as well as any other air leaks causing the wrong ratio air/diesel mix. There are no fault codes on the diagnostic equipment showing anything wrong, and the vehicle milage is 126k, and runs like new when working correctly. Just thrown £127 at this diagnosis but it is somewhat incomplete, but in an attempt to get this thing repaired must try repairers recommendations so have priced full exhaust at £849 inc vat at Janspeed Salisbury(cheaper than main dealers supply only price...), and air mass sensor £70.00 inc vat fitted. Any ideas?????

what year is it?

2004

After reading your e-mail, i had excactly the same symtoms with my 03 ducato. I changed egr valve (which was faulty) made no diff, then replaced air mass sensor. Replaced the cat which you advised, cured fault....Thanks mate....