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Discussion Starter #1
Hi everyone,

I need some help with my 2007 Passat B6 TDI PD BMR, I bought the car with the tank lift pump not working so to start the engine I needed to crank it for at least 30 sec, I believe that method has been used for a while before I bought the car. After I replaced the lift pump i still had problems with starting the engine especially if the car was sitting parked for 2-3 days, in order to get it started I had to cycle the key 2-3 times and even then it would start shaking for a couple of seconds.
Yesterday when I started the car it run for approximately 10 sec and then it died, i cannot start the engine since then, there are no errors present, the lift pump works fine, it pumps approx 3l of fuel in 1 minute at a pressure of 10 psi. Could the tandem pump just died? I`ve also noticed that on the return line from the tandem pump to the filter there is very low pressure as it will only put out 2ml of diesel per minute.

Thank you.

LE: I just found out that my father has fallowed a recommendation from a "mechanic" without asking me first, the "mechanic" recommendation was that he could check for leaks by using compressed air - so he did, he applied compressed air from a compressor to the intake of the tandem pump for a few second at a pressure of around 30 psi, he did not start the car after putting everything togheter but he primed the system once for 30 sec using the VCDS, maybe that explaines that when I started the car it run for 10 sec and then died after using any left over fuel - could that compressed air damage something inside the tandem pump or not it`s just air in the system ?
 

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Discussion Starter #2
the issue has been fixed, and maybe this will be helpful to someone in the future here how it got fixed:

unfortunately the purge with VCDS on channel 35 by activating the lift pump was not successful on its own, in my case there was a small air bubble stuck somewhere in the tandem pump or high pressure line and I was able to purge it out by activating the lift pump while I was pumping from the return line with a vacuum pump.

now I still have the initial problem with the sytem losing prime, as I put a piece of tape on the transparent hose immediately after the engine stop and after 3-4 minutes it doped 1.5 inches, also with the engine at idle I saw allot of small bubbles coming through the return line as seen in the short video and also after 10-15 seconds after engine stop

is there another check valve (non return valve) on this system other than the one on the lift pump itself? I saw something in the head of the fuel filter, there is definitely something with a spring in there - if someone can help me with that please

- with the engine running
- after engine stop

20190817_105017.jpg
20190817_105020.jpg
 

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Hi Mate,

did you get to the bottom of this? I have the exact same issue, long long crank before starting
 
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