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Intermittent Misfire Issue

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Old Feb 22, 2024 | 09:30 AM
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JBenzito's Avatar
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2014 C300 4Matic
Intermittent Misfire Issue

Looking for some help on this one. Last couple weeks been getting misfire on cyl 4. Replaced coil pack and did all plugs. Seemed to fix the issue. Couple days later engine light blinking and misfire is back. It’s not constant and driving me nuts. It’ll run fine and out of nowhere start misfiring and running like crap. If I pull over, shut off car, and start back up, running smoothly again and engine light off. Only codes that show are P0354 and P0304. 2014 C300. Any help is greatly appreciated.


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Old Feb 22, 2024 | 01:45 PM
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W212 MY'14 M276-3.5NA @75kMi
"o-i-h" misfire source

Originally Posted by JBenzito
Looking for some help on this one. Last couple weeks been getting misfire on cyl 4. Replaced coil pack and did all plugs. Seemed to fix the issue. Couple days later engine light blinking and misfire is back. It’s not constant and driving me nuts. It’ll run fine and out of nowhere start misfiring and running like crap. If I pull over, shut off car, and start back up, running smoothly again and engine light off. Only codes that show are P0354 and P0304. 2014 C300. Any help is greatly appreciated.

Your scanner is saying the coil circuit connector is bad.

I am sure you have looked at it well already... so now check for "oil-in-harness" around your engine bay... ECU, Lambda.

Reset faults, Reboot the car, reset once again.
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Old Feb 22, 2024 | 09:50 PM
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If you bought coil packs off of amazon or ebay that claim to be "original," they are fake replicas including the packaging. Ensure you purchase OEM/replacements from a reputable seller.
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Old Feb 23, 2024 | 01:18 PM
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Will check that harness for sure thank you! Yes I bought the coil directly from Mercedes but thank you for the advice. Never did trust Amazon lol.
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Old Feb 23, 2024 | 02:33 PM
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W212 MY'14 M276-3.5NA @75kMi
Originally Posted by JBenzito
Will check that harness for sure thank you!
Yes I bought the coil directly from Mercedes but thank you for the advice. Never did trust Amazon lol.
So this is a replacement MB Coil that ECU is still flagging as bad ... that means it is the circuit that's bad, not the coil itself.


We can summarize candidates as:
  • deffective harness connector at coil
  • (oil-in-harness ?)
  • ECU bad output MOSFET
  • (marginal GND connection)

🤞
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