Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi, without performing some tests for ignition spark and fuel pressure it is hard to say for sure what may be happening but the symptoms you describe sound very much like a faulty fuel pump relay. When the car won't start the fuel pump relay can be removed and bypassed to test for a faulty relay or you could simply replace the relay and see if it fixes the problem.
Let me know if you have any questions.