Power loss after changing gas from 91 to 89.
 

My 8 has around 2100 miles and I thought Im gonna try a "lower octane gas" thing.

However, I've experienced a "power loss in entire powerband". (DSC/TCS on and off)

My 8 seemed like it doesnt wanna do the way it does.

I've also heard some weird metal sounds from the engine when its accelerating.

I've just checked my oil and tire pressure, but they are fine.

What do you guyz think? Too early for lower octane gas?

maybe pre-ignition because of lower octane gas? Does it sound like you have bb pellets in your engine?

I think I had about 6k miles on mine before I switched. Mine does the exact opposite; using 91 octane makes it sluggish. Mine actually runs better with 87; idles smoother, accelerates better, better gas mileage. Maybe I just got lucky with my particular car, since I know not everybody seems to get the same results.

Oh, and I totally recommend you use Shell gas if you aren't already. I use Shell regular exclusively.

hmm...kinda, but only in high revs...?

oh..yeah..I was expecting that, too.

I guess Im gonna stick w/ 91 for a while and see how it runs.

I tested 87 from Shell and got pinging under extreme acceleration.... should stick with 89 maybe.

ignition problems are probably what you're expirencing, more than bad gas. the compression ratio is only 10:1.

If you were driving through the mountains the high altitude and/or grades could explain it. I've run 87 octane at sea-level up into triple digit temps and haven't had a problem. Your engine may also be running somewhat lean for some reason. Are you getting unusually good mileage? Another possibility is that your vehicle got the hotter plugs installed back before the M-firmware fixed the flooding issue. Or, maybe you just got a bad batch of gas.

Did you revert to 91 octane and have the problem go away?

Yes, I mixed half tank of 91 octane with the remaining 87 half tank and problem went away. Could have been a bad batch of gas as I did use 87 before... but maybe did not push the car that hard those days (now it happened just before the friendly "beep" in 1-2 gears ;)) Now I'm good, almost finished that blended gas tank and filled with Shell 89. Still no problems, so that points to the bad batch of gas as well. Did not notice improved milage - I am between 17 and 19 mpg but car just made 5000 miles today - hopefully will improve a little more.

PS car is 3 month old and came with M flash, so it is leaner. The A/F is about 14.5 to 14.9 when driving.