One of the most common causes of starting, drivability and performance issues in Volkswagen TDI diesels is fuel system restriction -- at the fuel filter, at the fuel tank, or anywhere in between. Dr. Dan of Dr. Dan's Biodiesel explains how and why this happens, and what to do about it. Fuel system plugging is usually caused by contamination from dirty, unfiltered diesel fuel, but biodiesel often gets the blame! Dan explains the various causes, symptoms, and consequences of fuel supply restriction in TDIs and takes us through the process of diagnosing and repairing a restricted fuel system on a 2000 VW Golf ALH TDI.