Hi all, ongoing investigation about random stalling and cranking but no start issue with my 2006 Octavia mk2 PD TDI BKC engine. I'm looking for a fuel flow chart for the fuel filter housing because something starge happening, there are 4 fuel line conectors but I can't find any marks which goes where. Checked the in-tank sender pump, looks okay as the supply pressure is about 0.5 bar (between sender pump and fuel filer) when priming but engine not running, however the pressure jumping up to 2.5 bar when engine started and idling, goes up to 3 bar when revving. In normal operation I think this is impossible to happen and this back pressure possibly coming from the tandem pump and working against the sender pumps 0.5 bar supply.

The other strange thing, there is zero pressure between the fuel filter and the tandem pump intake point. Checked tandem pump pressure, 5 bar idling and 7.5 bar at 3000rpm.

The culprit I think around the fuel filter, either blocked or/and pipes installed in wrong order or the non return valve stuck open or close in the fuel filter housing.

First I want to make sure the pipes are in  correct order bu I can't find flow chart for this engine.

Please someone help me to understand what's going on and with a correct flow chart pic, this is the current fuel hose setup. Red arrows  fuel from tank to tandem pump, green arrows return lines from tandem pump to tank.Other thing , if the hoses in wrong order  the tandem pump maybe receiving unfiltered diesel, god knows how long ago...

Found a cracked fuel line to the tandem pump. Replaced the fuel filter too, the old one was pitch black, probably not chganged a while ago. Primed the system with activating the sender pump, the car now start and idling fine so the filter hoses could  be in right order.

Further investigation on the fuel system as the fuel gauge was not working. For checking the wires for continuity I removed the speedo cluster and found out that there was a bent pin. Looks somebody butchered around here before and pushed back the loom connector carelessly. Staightened the pin  and voila, the gauge working again.