I have a 1991 mercedes 350sdl with 205,00 miles. The car was running fine til a week ago. When I turn the key to the ignition, I get a loud screeching sound similiar to the sound you get if you turn the key when you are in park and the car is already running. The car will not start at all. The radio,air, and lights are working. Would appreciate any ideas of what might be wrong.
It sounds as though the starter gear is not meshing with the flywheel.
I agree that the starter drive may not be correctly engaging the flexplate.
Try this. Manually rotate the engine a few degrees clockwiuse as you stand in front of the car by turning the fan or any other accessory you can move. Be careful of getting your fingers caught under the drive belt. Once you’ve rotated the engine try starting it again. If your noise goes away you almost certainly need a flywheel / flexplate.
Thanks for giving me some idea of what might be happening.