Does the mixture control unit flap move freely? If so, and it deflects while you crank the engine but there is no fuel going to the injectors, then I would suppose either: (1) fuel pressure is very weak due to defective pumps or fuel filter, or (2) the fuel distributor has a defect and is somehow not passing fuel.
My advice to anyone with a drivetrain issue is to search this forum and maybe submit a new post there, as peachparts is much larger than this R129 forum.
I have a good, used mixture control unit from a '92 300SL available for sale. Email me if you are interested.
