I'm wondering how you know what battery acid smells like. Not being a smart-ass, genuinely interested.

Trying to think how a metallic/scraping noise could result in a burning odor and then a CEL. Do you have the ability to see when the misfires occurred?

I was thinking if you might have a mechanical problem with your alternator. That might cause a metallic noise and a burning plastic or even electric odor. Not sure how the misfires or fuel pump issues are related but obviously fuel issues could cause misfires and misfires are sensed using, among other things, knock sensors.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim