Did you happen to check the fuel return line (and if your car has a valve at the tank, may want to make sure it's ok and air blows freely one direction, (back into the tank from regukator).
I also have not ruled this line out to be an issue with my 300E / 2.6. When I first removed the fuel return line and tried to blow through it, I almost could not, as it was very difficult. I removed the gas cap (which is pressurized) and some pressure escaped, but when I repeated the test with the gas tank removed for cleaning, it was the same, difficult to blow through. So, I replaced the fuel valve at the tank, and it seemed to make a difference as to blowing through the line, but I still have "too much fuel" that keeps flooding my engine....and yes, I have made many checks and have purchased many new parts along the way after a complete head rebuild.
My next test will be to bypass the fuel return line with a seperate line on the outside of the car. Fuel pressure regulator has been changed with used one off a good working engine, but no change.
Hope this helps, and I will let you know the resultsof my fuel return test.
Take care, and good luck.
'87 300E | 2.6 engine
Artic White - Navy blue interior, chrome rims, very clean and sharp!
The rest of my collection are just cars and trucks...no more "automobiles"...