1996 Mercedes Benz 500sl fuel pump

There are a few things to consider with this issue. First, your dad may be right. A Mass Air Flow sensor can definately cause this and will not always set a check engine light. If you live in a particularly dusty place this could be the case. As for the mechanics comment on fuel filters, MB recommends a new fuel filter every 60k miles. Not only could this be your cause, this would be the cheapest and easiest place to start. And more than likely you need one anyways. Also there is a known issue with fuel pressure regulators leaking internally on this vehicle. The faulty regulator will cause problems similar to yours. As for the fuel pump. I have seen very few fuel pumps replaced on 129 chassis of SL's. It is possible that this could be causing your issue however this is very expensive to replace and I would be very hesitant to go after this first. Many times when a pump goes bad it begins to hum and make excessive noise. You can ohm out the pump with a multi meter to check for high resistence as well. I however do not have the figures for spec on this.

you also mentioned the fuel pressure regulator might be leaking? how do I tell if it leaking and how do I replace it? it is hard?

thanks

This is a specific faulty part so it will be necessary to check the part # to see if it is part of the faulty batch originally shipped. The faulty part # is: 000-078-15-89 (Brumme production code 06.95 and 12.95) The fuel pressure regulator is located as illustrated below. Diaphragm Pressure Regulator #40

It will be on the driverside front of the motor. Along the fuel lines. You should see the part number on the regulator