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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 08-25-2016, 09:55 PM
nuron nuron is offline
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Location: Seattle
 
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Mein Auto: E90
What could noise be?

Meant to type "what could this noise be." Took a video--hope you guys can help me pin point the deep knocking noise (hope it's not a rod knocking ).

https://vid.me/DMJc
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  #2  
Old 08-26-2016, 06:21 AM
Al Kazaz Al Kazaz is offline
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Location: Caroga Lake, NY
 
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Mein Auto: E92 328i xDrive
Does it change in frequency when you rev the engine? If it does, then it sure sounds like a bad connecting rod bearing to me.

Al
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Old 08-26-2016, 11:55 AM
nuron nuron is offline
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I'll have to check that next time I hear it. The noise doesn't occur all the time, and it doesn't occur during cold start idle.

One other thought is maybe the previous owner filled it with low octane gas. I bought this car last month and haven't filled it with gas yet (wanted to empty the tank so I can jack up the car easier for the diff fluid change haha). I'll try putting some Shell or Chevron premium in there and see if it persists.

Last edited by nuron; 08-26-2016 at 12:09 PM.
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Old 08-26-2016, 05:21 PM
Al Kazaz Al Kazaz is offline
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Location: Caroga Lake, NY
 
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Quote:
Originally Posted by nuron View Post
I'll have to check that next time I hear it. The noise doesn't occur all the time, and it doesn't occur during cold start idle.

One other thought is maybe the previous owner filled it with low octane gas. I bought this car last month and haven't filled it with gas yet (wanted to empty the tank so I can jack up the car easier for the diff fluid change haha). I'll try putting some Shell or Chevron premium in there and see if it persists.
Not saying that's the problem, but during the early stages of bearing failure no knock on cold start is normal as the more viscous oil phase absorbs the shock.

I doubt it is the fuel. The ECU will always prevent detonation by retarding the timing if it detects an ignition knock. The effect of low octane fuel is lower maximum power as the ignition timing cannot be advanced far enough for optimum output while simultaneously preventing detonation. Somewhat counter intuitively, a higher octane rating is a "slower" burning fuel as it resists premature ignition from compression alone.

Al
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