1998 SLK 230,
just went out of town wife called and stated the car cranks over but never starts. After crankinf for 5 sec she said there was a noise like a swoosh sound??? She had just fillled the gas tank and added a 1/2 quart of oil to top it off. Never had a problem before

 

could be clogged fuel filter or faulty crankshaft position sensor.

have somebody read the fault code and check fuel pressure.