Well, I got the connector. Fuel pressure ramps up to 55 when key is cycled. Pressure stays at 55 with engine running. Drops to zero within 7 seconds of engine cut off. Clamped off supply to fuel rail. Pressure holds, so it should not be fuel rail.

Manual says slow drop off is check valve in pump. Fast drop off is check valve in filter. I presume seven seconds is fast? But I've changed filter twice - with MB unit on now. Not sure of what their definition of "fast" was so we went to clamping lines at filter. Clamped line at filter to fuel rail - pressure holds so it should not be any leaks in the fuel lines. Clamp on line to "Can" - no difference, pressure falls off. Clamp on line to "pump" - pressure holds. So, this indicates check valve in pump is bad? Said check valve choosing to fail just when the filter was changed?

Is my analysis above valid or am I missing something? Don't like coincidences. BTW, if I do get a new pump - is it Mercedes only or are there good reliable alternatives for less money?

HP