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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > Burning, acrid interior smell.

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      01-22-2020, 08:56 PM   #1
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Drives: 2010 328i Xdrive E91
Join Date: Feb 2019
Location: vancouver bc

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Burning, acrid interior smell.

So this is fairly uncommon, and happens to different degrees, usually only very briefly. I can't pinpoint when/where under what circumstances it's triggered:

It seems to happen most often when I go down the ramp into my underground, which does indicate something possibly dripping/falling onto a hot surface.
But it's also happened on flat ground, driving around, although NOT when i drive smooth or consistently i.e. commuting on the highway.

My interior gets a blast of a "burning" smell every once in a while. I don't believe it's engine/fuel/oil/exhaust related. Smells more along the lines of plastic or rubber?

It DOESN'T come through the vent system.
AND it doesn't smell under the hood, nor is there any visual indication (i.e smoke).

I do have some very minor oil sweating around the valve cover, but certainly not enough to drip on any belts, as far as i can tell.

I've seen an issue with a soundproof/firewall disintegrating, described as "burning crayons" and I'm leaning towards that but don't want to tear apart my interior if it's not necessary.

Any other theories?

Car is a 2010 E91 (328i wagon)
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      01-23-2020, 01:06 AM   #2
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Drives: BMW 330i 06
Join Date: Apr 2012
Location: TN

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There are multiple recalls for electrical components, notably the blower motor in the ventilation can overheat. The oil separator has a heating element in some models that also can overheat (not sure if you have it, was mostly on early e9x).

Check for signs of water infiltrations in the door and around the dashboard (wet carpet in the footwells), as well as in the trunk. These are the common areas.

I would not rule out an oil leak dripping on the exhaust manifold. It is common and matches the symptoms about being sensitive to acceleration/turning, despite the lack of smoke being atypical. Inspect the exhaust headers for 'wetness'.
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      01-24-2020, 12:29 PM   #3

Drives: 06 325i
Join Date: Apr 2013
Location: Los Angeles

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Is the smell coming from under your dash?

I was getting an awful plastic smell just on occasion like the burning crayons and didn't know where it was coming from. I removed both panels under the dash (above the footwell) and was able to smell it more; but it was only happening once in a while.

I eventually traced to the e-box ventilation duct. The ebox under the hood has a duct running through the firewall under the dash and there's a fan to circulate air and cool it. I noticed when this fan turns on, that's when I get the whiff of the horrible smell. I removed the ebox lid and sure enough that's where the smell is coming from. I don't think it's burned wires, but the plastic of the ebox itself degrading and causing the smell, then when the fan kicks on it blows that smell into the cabin, specifically concentrating under the dash.

Ideally I'd like to remove the ebox and vent duct and wash it out, however that's too time consuming. I am going to give it a quick wipe with some spray cleaner and a rag (mine's full of dust inside) and then toss a paper air frehener inside.
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