My friend has a 1998 ML320 and it has a strong smell of gas fumes especially when starting the car. It takes about 10 sec. of cranking before it starts. Took the car to MB dealer for service and they said the check valve in the fuel pump was bad (based on their claim of a failed leak down test). $800.00 dollars later for new pump and filter, it still does the same thing. I am wondering if there could be a cut out fuel injector or possibly (if it has one) a leaking cold start valve. At times while driving the car it will start running rough as if it is only running on 5 cyls for short periods of time and then clear up.

Thank You