2003 Mercedes starting problems

[micali]

Engine Performance problem
2003 Mercedes Benz ML320 6 cyl. All wheel drive (I think) - Automatic 98879 miles

We've owned this vehicle 4 or 5 years and never had a problem with it starting. My wife drove it to work yesterday like usual. When she tried to start it to drive it home that evening it wouldn't start. It just turned over like it was out of gas but it had nearly a full tank. It is a gas powered vehicle, not diesel. She tried several times and the same thing happened. I got there about an hour later and, when I tried, it started on the first try like it always had done previously. She had to make a stop on the way home and after leaving it for about 45 minutes it did the same thing again. I tried again immediately after she had just tried. After 4 attempts it started and she drove it 15 miles home with no problems. It has always started on the first try. We have not driven it or tried to start it since she got home last night with it.

[micali]

From what I can tell it's the CPS.

[eclass]

yes, crankshaft sensor. to test- verify with scan tool, look for rpm signal- if there is none then suspect sensor. you could also verify that there is no spark, injector pulse, or fuel pressure.