I'm having intermittent problems with my E320 cranking but not starting. It has also stalled twice, once at a stoplight and once in a slow turn. No check engine lights.

The pattern I've observed is that it starts fine when it is cold, but after it has been driven for a while (e.g. 10 mi), it will not start again unless it cools down for at least a couple hours. When I drive it, it runs smooth, with the exception of the two stalls. But then again, I let it sit for a few hours and then it starts fine.

The first thing I tried was a new fuel pump relay, but that didn't make a difference.

Any ideas?