I have had issues with my E350 that I am sure are fuel related. I will try my best to explain. When I cold start the car I turn the key to position 2 measure the fuel pressure which is 55psi. Every now and then after a 20-30 minute drive I return to the car to crank and it stumbles and dies then refuses to start for about 15-20 minutes. I replicated the issue and as I suspected the fuel pressure on the rail dropped to less than 10 psi which I feel caused a vapor lock scenario which explains why this stumbling and dying issue only happens when the car is up to temperature. Another thing I noticed is that the fuel pressure generally runs around 35psi when the motor is warmed up. So i dug into the fuel system and did a dead head pressure test on my fuel pump and it showed 85psi which is good. So being close to the fuel filter service (79000miles) I went ahead and purchased a new one. I have installed it and cranked the car up and as usual on cold start it pressures the system up to 55 psi. I bled the pressure off of the system to read pressure once the car was warmed up and to my dismay I am again showing 35psi. I thought maybe an injector is stuck open but I dont see that being the case. I have not driven the car since the filter swap but I am concerned that im missing something. I cannot find a fuel return line going back to the fuel tank I dont think this system has a fuel return. i have also done a pressure drop test and I loose about 8 psi in a couple of hours. I am mechanically inclined and have worked on cars before but this is my first mercedes. Ive had a host of other issues ive fixed since obtaining this car and the fuel issue is getting the best of me.