[Dicksilver]

1999 New Beetle TDI cranks but will not start. I noticed some air bubbles in line from filter to injection pump, so replaced fuel filter, sucked fuel thru with Mityvac, connected, still cranks but not even a sign of starting. What next?

 

[1Kevin]

Try slightly loosening of the the fuel lines at the fuel injector. Wrap a thick rag around the nut. When the rag is wet the engine is ready to start. Did you have this problem before you changed the fuel filter?

Big bubbles or little bubbles? Maybe one of the return lines or the pump seals are leaking.

 

[chittychittybangbang]

Some possibilities, do you briefly see the glow plug light when you turn the car on? If not at all, relay 109.

fuel shut off solenoid - this is the knob on the pump head

fuel leak along the line which is causing the bubbles. If the leak is bad enough it can cause the pump to lose prime.