Discolored ignition coils on my x5 (n55)

[snowracer21]

I have a 2015 X5 35i (N55), with roughly 105k miles. I replaced the spark plugs and coils at 80k due to a rough idle when cold. Delphi coils and Bosch plugs, ordered from FCP Euro.

Prior to changing coils/plugs I'd see 26-28mpg highway, and ~22mpg around town. After replacing both I'm now seeing ~18mpg around town and 21mpg highway. My OBD scanner doesn't show any misfire codes, however I think ISTA may show different.

I decided to pull the coils and plugs to check my work and make sure everything was connected properly. In my stupidity I realized #6 spark plug (rear of the engine) was not torqued sufficiently. I'll chalk this up to the difficulty getting a ratchet in that tight spot. More alarming though: while coils 1-4 looked brand new, coil #5 had a bit of carbon buildup, and coil #6 looks as if it was left out in the rain for a year.

Unfortunately I didn't grab a photo of the coil, but it's either a buildup of rust, or burnt oil. All 6 spark plugs (including 5&6) looked good though.

I'll know if I fixed the problem after next fill up and calculating the MPG, however I'm wondering if there's maybe a bigger issue in cylinder 6? Anyone have any insight?

[stocktree]

Are you able to look down the sparkplug hole?
This guy recently found a surprise.
https://f15.bimmerpost.com/forums/sh....php?t=2038752

[snowracer21]

Originally Posted by stocktree

Are you able to look down the sparkplug hole?
This guy recently found a surprise.
https://f15.bimmerpost.com/forums/sh....php?t=2038752

Yeah, and fortunately I didn't see anything that would cause a concern

[stocktree]

Was the 6th coil oil soaked?

[snowracer21]

Originally Posted by stocktree

Was the 6th coil oil soaked?

It wasn't soaked (wet) in oil, however the coil was covered in an orangeish buildup...I'm assuming either burnt oil, or rust?

[Hop74]

Originally Posted by snowracer21

It wasn't soaked (wet) in oil, however the coil was covered in an orangeish buildup...I'm assuming either burnt oil, or rust?

I'm guessing burnt oil. Mine was soaked with oil and after wiping the oil, also looked deep orange/brown. I was smelling burnt oil for quite some time. As a result, the seal around my coil seemed to fail. It came out very easily when i pulled it.

Maybe something similar happened with you because the plug wasnt torqued all the way down, it caused the seal on the coil to also fail prematurely? Simply guessing...

[tlow98]

Did you check the gap on the plugs? And you used OE BMW plugs or the NGK equivalent?