My 99 ML320 has starting having problem starting. I turns over fine but does not start. I have read that two common failures are the fuel pump and security. I have replaced fuel pump and tried all of my keys when the problem occurs. Also, when using my key to unlock the drivers door, (not the remote) the alarm goes off. Can this be a sign of security failure? When it decides not to start, it typically last 24 hrs and then it is fine. Has anyone else had or heard of this problem? Also, I did system scan and no codes were present. I have also read that when replacing the pump, that the 3 fuel lines as well as filter should be replaced. I did not do that. Is the regulator part of the filter? Any help is appreciated!