The problem is definitely electrical in nature....
Either One of Three things....
#1 Fuel pump relay about to die... There may be a cold solder joint, or other failure in the relay that will cause it to work intermittently, or finally quit.
#2 The actual fuel pump - it may be failing. But I would think that if the pump is failing hesitaton, or rough running due to inconsistent fuel pressure would be present. Does the car exhibit any of these symptoms?
#3 A ground somewhere may be loose, and making contact some of the time... This would lead to more of an intermittent no start / stalling in motion problem, as a bump in the road may loosen the ground and cause the fuel pump to stop pumping fuel while the car is running. Chances are this is not the case in your car because you have only mentioned intermittent starting issues.
You mentioned your tech recommended replacing both the relay and the pump. Did he test the pump by jumping the relay contacts to send 12V directly to the pump. - With the seat out or even with the first aid kit open you should be able to hear the pump.
The relay is a simple fix, and chances are will cure the problem. Especially if the pump tests out ok. Did the tech give you any reason for wanting to replace both? Or is this more of a preventative measure in case the fuel pump is on its way out anyway?
Also make sure the fuel filter is replaced when the pump is replaced.
Hope this helps,
1990 500sl R129 - 76k Original Miles - New project - Follow the saga http://90r129.blogspot.com/
1990 190E 2.6 148k mi (sold)
1989 420 SEL 246k mi (sold)
1995 C220 175k mi (sold)
1992 190e 2.6 74k original miles (sold)
2000 c230 Kompressor 122k miles (RIP)
1996 C220 149k mi (sold)
2000 C230 Kompressor Sport 127k (sold)
2009 Mercedes c300 4matic
2006 Mercedes s430
2005 Jaguar XJR
2003 Cadillac Escalade