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2008 ML320 CDI Crank Start Run Die

 
Old 02-26-2013, 11:48 PM
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08 ML320CDI
2008 ML320 CDI Crank Start Run Die

Hello,

My recently acquired ML320 CDI has developed an odd issue after I recently replaced the oil cooler seals last weekend (small leak, was annoying). I've put about 2K miles on this car since purchase (with zero issues, outside the annoying leak).

Anyway, here's what happens:

Unlock car, get in.
Insert key
Turn to Run
Wait for glow
Turn to Start, release
Engine cranks, engine fires (like normal), then dies after 1-1.5 seconds of running.

I can repeat those steps over and over and it does the same thing every time. Same if I use the other key.

Unplugging the pressure sensor for the common-rail causes it to run for about 3 seconds (and slowly stutters to a stop).

With my diagnostic readout, I can see fuel-rail pressure jumping up to normal numbers (and to be honest, the engine is starting strong). I can hear the electric fuel pump when I turn on the key (and got sprayed in the head by the bleeder on the fuel filter). Currently no codes.

Recently, after cleaning the intakes manifolds/plumbing/etc. of EGR goo...I was getting a "Exhaust Pressure High" code. I just presumed that it was due for a regen (and it wasn't in limp mode or running poorly).

Any thoughts on this one?

It feels like electronic since it starts strong and acts like someone just shut it off when it does die. Literally drove it to work, parked it, and couldn't leave.

Thanks in advance!
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Old 02-27-2013, 02:43 AM
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08 ML320CDI
After doing some exhaustive research I saw mention of someone with a w164 and a OM642? claiming that excessive back-pressure caused the vehicle to start, run, and then quickly shut off. The exhaust back-pressure sensor located just to the right of the turbocharger near the EGR valve may be culprit.

I am going to pop the VNT actuator loose, open the vanes fully, and see if the engine fires. It is of course also possible that this sensor (or the wiring to it) has failed. Considering that the vehicle was just operating normally, I suspect the latter.

I will report back tomorrow with any findings. If anyone has any other items to check, please feel free to chime in.

Thanks,
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Old 02-27-2013, 01:22 PM
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08 ML320CDI
Update from some morning diagnostics.

The back-pressure sensor appears to be the root cause of the no-start situation. Unplugging the sensor results in successful run and start. Plugging this sensor in while running turns on the MIL and sets a code related to this sensor being low/high.

I am going to pull the sensor out and (likely) replace it.

Hopefully this helps someone else in the future. Simply unplug the sensor right beside (drivers side) the turbo after removing the plastic cover/shield. Vehicle will fire up and at least run (not sure if it's going to go to limp mode or not).
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Old 02-27-2013, 06:42 PM
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08 ML320CDI
For reference,

Sensor showed 3.83V with key on, engine off, on signal wire. It should have been closer to ground (0V).

The Gnd and 5V pins showed good even during cranking. The signal pin had no continuity between it and ground or 5V (as if there were a damaged wiring harness somewhere).

It appears this sensor simply gave up the ghost and me knocking it around while cleaning the intake manifolds finally finished it off.

I ordered a replacement from the local dealer and will pick it up Monday. The vehicle appears to not enter limp mode with the sensor disconnected.

Vehicle has ~175K miles and this 'appears' to be original.
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Old 12-17-2013, 03:54 PM
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Thank You Brandon. I'll keep that diagnose on my mind because I have a similar engine OM642 (3 litre V6) in my 280 VDI year 2006
Br Hannu
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Old 06-25-2018, 04:19 PM
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Mercedes-Benz 500E
Just found this thread and it fixed one I have in the shop right now. No codes and problem would come and go for no reason I could find. Could find no issues with fuel pressure. Did find and oily substance in the connection but since the sensor monitors the exhaust I can't figure where it would come from. Very glad I found this!
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