OM642 (Bluetec V6) Intermittent "No Start"
 

My friend's vehicle has a problem: After driving and parking, when coming back to the vehicle, sometimes it does not start. It cranks just fine. The fuel filter was replaced recently, so I doubt it is a fuel issue. Is there a cam or crank position sensor that could be going bad? Anyone know of this type of problem with their OM642??

Sensor failure common on most cars. Car does not restart until it cools off. Get a can of cold spray. Spray sensor. Car starts right up you usually have it. Thermal problem basically with the sensor.

It does have a crank position sensor.

I had this problem. There is a long posting in the archives. Either a starter not turning fast enough or sensor connections to the "tank" in the exhaust system.

Have you tried pulling codes?

These engines totally rely on the cam/crank sensors to know when to inject.
No signal = no fire

Sure sounds like a heat soak problem, that could affect either sensor.

Before shooting the parts cannon I would try pulling codes to see which one it is.

Cam sensor is super easy it is on top, right side bank between #1 and #2.

"Have you tried pulling codes" Yes and No.Yes, we did use a basic code reader, and no DTC's are present. And No, because neither my STAR system or Icarsoft MB II will work on this vehicle! Why not you ask? Because the vehicle is a 2008 Jeep Grand Cherokee with a Mercedes-Benz engine/transmission (OM642/722.6). I figured that other MB chassis' might have a similar problem, as the engine is the same. The problem is that I doubt any MB specific scanner will communicate with the vehicle (I have not tried).

I do thank everyone for the suggestions on what might be the problem, and my friend has a can of R152a to spray on the sensor/s next time the car won't start. That is quick, cheap, and easy. Let's hope it is a bad sensor, that will be easy to fix......Rich

You are correct in that the Mercedes’ icarsoft will not read the Jeep , I have an 06 3.0crd GC and I use the icarsoft bcii (think it is) and this covers Dodge Cadillac Jeep etc etc.
When I fitted an exchange turbo on mine I unplugged the cam sensor to stop engine firing so I could get some oil pressure up to turbo… did not make any difference the engine fired and ran !!!.
Cranking speed has been mentioned by DDAY and this needs to be 200rpm or ecu will not fire injectors .
Crank sensor is above starter motor and easy on mine to get at as mines UK right hand drive .. either from above fender or remove arch liner to access are your options.
From my experience with mine with faults and codes you may well find it may have a pending crank sensor code but no other warning lights showing to let you know that .. it’s a Jeep !! Seriously they are odd vehicles.
But the symptoms certainly fit bad crank sensor.
I often see posts where owners go to parts stores and these stores scan vehicle free of charge but I cannot remember the name of store.. Chrysler /Dodge /Cadillac scanner should do it as they use same protocol EDIT … went and looked this up
“ If you can. Take it to the local auto parts store. Advance, O'Reilly, Pep Boys, etc.”
Also cheap setup called Torque ( Torque pro or Torque app ) you run on a laptop that’s vin specific ie one vehicle only for something like around $49, you can program new keys on the Jeep and do all sorts of things with it

Thanks for the great info. I had a 1998 E320 that had a bad crank sensor, but the engine also died without any warning several times while driving. The Jeep engine has not died, but only fails to start after driving it a while. I would think that if a crank/cam sensor was intermittent, it would exhibit both failure types.

They normally first play up on a hot engine ie failure to start until engines cooled down.

There was a service bulletin for the crank sensor on these Jeeps. I wasn't sure if mine had been replaced so I bought a spare just in case. I've been carrying a spare for over 10 years, of course never had a problem with it.

Some reading regarding the instructions/TSB:
https://www.jeepforum.com/threads/crd-crankshaft-position-sensor.3717857/

Best scan software:
Appcar DiagFCA (PC)
OBD JScan (android)

You are the man!!! Thanks!