You need to go through the diagnostics of the fuel system to rule it out. Check your eha numbers and your duty cycle. Do a search there is a lot on this.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)