Best way to troubleshoot Power / Turbo issues
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Junior Member
Joined: Feb 2018
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GL320
Best way to troubleshoot Power / Turbo issues
Hi all,
I've got about 275k on my 2007 GL320 CDI (OM642) and I've been nursing it for a while. Have had to do the swirl flaps bypass and unplug the exhaust backpressure sensor and EGR valve. The car drives ok but the turbo is disabled with all these things unplugged and bogs down when accelerating onto the freeway and climbing hills. I did try to replace the backpressure sensor and EGR valve and also the turbo actuator based on codes that were thrown but that hasn't solved the problem and the car goes into limp mode if I leave everything plugged in. I'm thinking the turbo itself may be bad and I'm wondering the best way to test the turbo to see if I need a full unit not just actuator. I have the Autel MP808 that can run most of the same diagnostics as STAR.
Any help appreciated.
Max
I've got about 275k on my 2007 GL320 CDI (OM642) and I've been nursing it for a while. Have had to do the swirl flaps bypass and unplug the exhaust backpressure sensor and EGR valve. The car drives ok but the turbo is disabled with all these things unplugged and bogs down when accelerating onto the freeway and climbing hills. I did try to replace the backpressure sensor and EGR valve and also the turbo actuator based on codes that were thrown but that hasn't solved the problem and the car goes into limp mode if I leave everything plugged in. I'm thinking the turbo itself may be bad and I'm wondering the best way to test the turbo to see if I need a full unit not just actuator. I have the Autel MP808 that can run most of the same diagnostics as STAR.
Any help appreciated.
Max
Member
Joined: Jun 2016
Posts: 161
Likes: 33
From: Orlando, Florida
2005 E320 CDI (SOLD); 2008 ML320 CDI 4MATIC
What's your DPF soot/ash saturation? That's highest mileage I've ever seen on a om642 that wasn't in a Sprinter. Mercedes shoe-horned them into cars & SUVs so they have smaller oil pans & air intake surface areas which really takes it's toll on these variants unless oil changes every 2 to 3k miles w/ superior oils like Liqui-Moly or Pentosin & air-filter changes almost as frequently. Shine a flashlight down into your engine from oil fill port & get a picture of timing chain tensioner and then start engine to observe for excessive blow-back coming up thru that port while engine is idling. If tensioner is fully extended, then timing chain will likely be stretched. I see massive expensive repairs in future unless you are DIY tbh to include DPF, timing chain, oil filter housing leak, CCV leak that will cascade into turbo seal leak where air intake plugs in [some buy a little time on this w/ an oil catch can] then that oil will drip onto swirl-flap actuator and turbo pedestal eventually ending up in engine valley where it will appear to be coming from oil cooler as it drips thru valley weep hole drain and starts marking it's territory wherever you park. Congratulations on keeping it going this long but unless you like self-torture, I'd recommend selling it asap.
MBWorld Fanatic!
Joined: Jun 2021
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From: New Hampsha
'17 GLS450, '14 GLK250, Grandpa's Roadster
Try to wiggle the shaft side to side. There should be some play, but not enough to make the compressor wheel touch the housing. If there is a lot of play but no touching, the bushing on the turbine side could be bad.
Is the compressor wheel damaged? If you can, get eyes on the turbine wheel, too, and check for damage. If it spins freely and there is no damage then it probably isn't the cause of low boost.
Is there a lot of oil in either side of the turbo? This won't necessarily affect performance, but it can damage downstream devices like converters and DPFs.
