Open the left compartment door. There is the priming pump with the fuel/water separator filter just below it. The filter more improtantly filters debris from the fuel. There is a T coming out of the tank and either 3 or 4 lines connecting to the fuel/water separator. Keep in mind that the separator uses centifugal force to create a vortex to get water out. Now my question. Where do all those fuel lines go? I am confused. I wonder if there is a return line to the tank. Can anyone give me a primer on the fuel pathway in this area?
I got dosed with bad fuel in a 2005 D4 last year...no manual...in the field...had to flush everything out and used a 12v fuel pump with a tube and copper pipe to suck all the crap out of the tank. Then, started taking the lines off and started blowing them out with compressed air. If memory serves, the ones to the rear go to the inlet of the tank and to the tank return. Of course I drained the separator, then undid the lines to the injection pump too...blew them out...while that was disconnected, I broke all the injector lines loose and cranked the motor to flush them. Put fresh fuel in and left the line to the injector pump off and turned the key on until it had fuel coming out...then I hooked that up again and cranked the motor until the lines to injectors were flushed...tightened them up, and she purred like a kitten. I hope that helps?
Maybe this will help. I will see if I can get the theory of operation for you.
Thanks to everyone. The responses were a big help.