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oddcarnut

OM 642 diesels

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No it isn't the next covert Piggy project, but our alternate tow vehicle is a 2007 Jeep Grand Cherokee with the 3.0L Mercedes OM 642 turbo diesel.  Any Champers wizards with these?  Ours suddenly refused to run and so far I'm striking out on why.  Pretty sure it is injection related.  So if you happen to have experience with these critters, please PM me.

 

Ken

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20 minutes ago, oddcarnut said:

No it isn't the next covert Piggy project, but our alternate tow vehicle is a 2007 Jeep Grand Cherokee with the 3.0L Mercedes OM 642 turbo diesel.  Any Champers wizards with these?  Ours suddenly refused to run and so far I'm striking out on why.  Pretty sure it is injection related.  So if you happen to have experience with these critters, please PM me.

 

Ken

 

burn it to the ground..  quickly.

I've been a Chrysler tech for 20 years,  does it even start?

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10 minutes ago, wvumtnbkr said:

Does it have spark?.....

 

LOL.  Those invisible, special diesel spark plugs, ignition wires and coil are really hard to find and trouble shoot!

  • Haha 1

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Did this ever get resolved?

 

I just went through a similar situation but with a 2006 Smart CDi, common rail 800cc 3 cylinder engine that was engineered by M-B. 81,000 kms, was parked because of low power. No start or firing by itself but could be coaxed to momentary life with a spritz of ether then quit within 5 seconds. Compression test showed two out of three down so I went through the engine. Reringed, had rust at the tops of the bores because of sitting so long, did the head, etc. Yes, I ported it while it was apart, just can't help myself!

 

Engine back together, still no start or even popping without ether. Checked low pressure fuel pump, 35 psi so good. Checked high pressure fuel pressure sensor reading, with key on, engine off. 0.035v when it should be 0.5v or so. Replaced sensor, now reading 0.565v key on, engine off. Cranked engine, reading went to 1.37v, indicating high pressure fuel pump is working properly. Spritz of ether, momentary reading of 1.585 volts as the engine started and went up to about 900 rpm before idling momentarily at 700 rpm then quitting. 

 

Engine acted like a gas engine that needed more choke. Compression is good and no smoke out the exhaust, so not enough fuel. Fuel rail is at proper pressure so that left the injectors or the ECU. Sent the injectors out for cleaning and testing. Failed due to low fuel volume after cleaning (ultrasonic on the tips only, no disassembly). Claimed that the Bosch injectors (same design as OM642?) had to be rebuilt by a specialty shop to get them working again. Rebuilt cost, $330 each or $800 new. Worth more than the car!

 

 I had six injectors total so I took the nozzles off my spares and checked them, only 2-3 of the 5 tiny orifices open enough to spray through. Soaked and cleaned, back flushed, etc, until I got three of the six up to 5 sprays; the others were up to 4, not perfect but still much better than the shop managed.

 

Reinstalled the three best ones, now trying hard to start, still needed a spritz of ether but only on the first try. Now started and idled at 800 rpm (normal) but quit after 10 seconds. After assorted starts and runs including carefully running it up a bit with throttle, it now starts well and and though a bit reluctant (might be normal for a Smart car) revs up to 3000 rpm (didn't try higher but could have).

 

Next step now that it's running is to check the fuel return rates and maybe do some more cleaning.

 

Your engine should have essentially the same sensors so hopefully these steps will help you diagnose why it's not running. Low pressure fuel pump would be my first suspect. Might also be your glow plug controller, should check for voltage at the glow plug connectors to verify. Be very careful and sparing using ether on a common rail engine.

Edited by mender
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