2009 W164 ML63 fuel system diagram pressure accumulator
 

I cannot find a diagram for the fuel system for my 2009 W164 ML63. Did Mercedes not do one? I only see the gas tank diagram. I am tracking down a P0191 high fuel pressure at fuel rail fault. Car runs great. Full power. Zero smoke. Sensor on rail was replaced resulting in a better idle. I am replacing the fuel pump control module under the back seat for good measure but I am thinking there should be a fuel pressure regulator/return valve by the fuel line into the fuel rail. I do not see it? I can't believe that pulse width modulation to the fuel pump is enough to keep a rock solid fuel pressure? Regards, Bo

I would advise to get some data with Xentry or equivalent. I DO NOT advise replacing parts with no proper diagnostics. HOWEVER I found a remedy to a similar 6.3 w164 by replacing the pumps.