merc vito wont start?

Hi, i have a 99 vito van which was fine until 4 months ago when i was driving alone it started chugging then finally stopped. A mechanic has had it ever since. He has changed the fuel filter, replaced all seals, sent the ecu unit off to be repaired, charged the battery but it still wont start. He said that it will start if he uses easy start but not by itself!??!?! :( Any ideas??