I figured out why I wasn't getting any bubbles. Since this was my first time doing the delivery valves, I didn't know that the valve seats (the bottom most part of the pump elements) are supposed to be oriented in a certain way. Each hole in the IP has a pin that slides into the notch on each valve seat and it's possible to install the valve seat at a wrong angle and push the pin out which will lead to blockage of fuel flow. That's what happened to me while I was doing the bubbling. The pin being pushed out really scared me, but then I found out I could take the side cover off on the IP and gently hammer it back in. I'm glad I caught this mistake before I reinstalled the delivery valves with the new seals.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL