My 2006 E320 TDI puts out an embarrassing amount of black smoke whenever I accelerate hard enough to cause a downshift. It is just a short (2-3 second) belch, but it is enough that I can see cars in my rear view mirror driving through the cloud. It just does not seem right for a car with 47K miles that has been taken care of very well.

Another important note: about 15K ago the dealer had to replace two glow plugs, the cylinder head (one of the glow plugs broke off as it was being changed), the turbocharger (it was making a bad noise), and the alternator. All under warranty, but now as the warranty is drawing near its end, I am worried that the smoke issue means I will be having problems again. Could it be related to my previous glow plug and turbocharger problems or is this normal? I am pretty sure I will be going back to the dealer, but I am interested in hearing the opinion of others as well.