1656 fuel transfer
 

First time on here. looking forward to being a member. thank you for any help. I am a benz tech at a dealer. I am working on a 2013 ML350 diesel. my fuel will not transfer from left to right in my fuel tank. I replaced the fuel pump and the transfer pump. II have inspected the transfer hose that runs between them and cannot find anything wrong. When I put fuel in the car the right half of the tank drains dry and the left half (the fuel return side) fills up until the car goes dead. Ive been working on these things a long time guys but this one has me stumped. The fuel feed and return appears to be working properly but the fuel WILL NOT transfer side to side! ANY SUGGESTIONS WELCOME. And if I can help any of you guys let me know> Thanks