I agree on the no Backfire on Diesels.
White Smoke can be Coolant or atomized unburned Fuel and you can often tell by the smell.
Sounds like something is causing a misfire.
Some big Air leak can cause a misfire.
A Headgasket issue can cause a misfire. Look up the symptoms of a bad Head Gasket in the DIY Section.
Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum
PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles
Try doing the Injector Cutout Test. To locate the bad Cylinder. If you find a bad Cylinder swap the Injector from that Cylinder to antoher cylinder and see if that Cylinder now has the problem. If the problem follows the suspect Injector to the new Cylinder it ias a bad Injector.
Try Changing the Fuel Filters. If that does not work get long length of 5/16" Fuel Hose a Container with clean Fuel draw the Fuel from the Container instead of the Fuel Tank.
Are you sure the Sucking Sound is coming from the Front of the Car. If not your Tank Vent could be restricted.