Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi Dick, my name is***** is not an easy fix. You need to be able to duplicate the problem in the shop in order to get an accurate diagnosis. The crank sensor and the fuel pump are two common problems that will give you this symptom. Assuming that they used an OEM crank sensor I would suggest they inspect the harness and the connector to the sensor. I'd also consider replacing the fuel pump relay. Ultimately the only way to get to the bottom of this is to have the car act up during testing. Either you aren't getting spark or you aren't getting fuel when this happens. First they need to determine which is missing (spark or fuel). Once they determine that they can narrow down the problem. I've driven cars for weeks with a fuel pressure gauge connected to the fuel rail and taped to the windshield in order to catch a malfunctioning fuel pump circuit.
Let me know if you have any questions.