Electrical & lights on 1991 Mercedes-Benz 560SEL

My car shut off when the engin is hot.The problem occurs on the highway or in the city.What can it be ,the fuel pump,the relay,the distributor..... Thank you for your time.

by in Amawalk, NY on May 16, 2010
3 answers
ANSWER by on May 16, 2010
An engine needs three things to run, mechanical integrity (which it must have or it would not restart), fuel and spark. To find an intermittent problem like this I "tee into" the fuel line and tape a fuel pressure gauge to the windscreen so I can monitor fuel pressure when the problem occurs, if fuel pressure falls off you then start tracing the fuel pump, fuel pump relay and sensors that allow fuel operation. I also drive around with a timing light attached to one of the spark plug wires, when the vehicle falters I pull the trigger on the timing light and see if I have spark if not I check the ignition system and wiring and sensors associated with the ignition system. Intermittent problems are hard to find and your vehicle has limited diagnostic capabilities. Understanding how each system works, having a good wiring diagram and volt/ohm meter and patience are required to trouble shoot this kind of problem.
ANSWER by on August 13, 2010
There is a fuel accumulator in the rear which is supposed to apply back pressure to the fuel line. If it wears out, the heat of the engine causes expansion and not enough fuel gets to the engine.
ANSWER by on September 24, 2010
I had problems with my 1991 560 stalling only in 104 degree weather. Changed the fuel pump relay and ignition module ($1700) and still had the problem . Engine always worked at the dealer. Small town mechanic let it idle until it stalled after an hour and found that the separate fuel system power take off from the positive battery terminal was loose. Problem fixed. We surmise that when the battery was changed the wrong nut was initially loosened in mistake for the real terminal nut and not tightened afterwards. It is often a very simple problem.
Related Items:
The fuel pump and/or fuel pump relay can fail, causing the car to crank over but not start. Proper diagnoses will be necessary to confirm if the pump or relay is at fault.
The instrument cluster, along with the turn signal and wiper combination switch, can fail.