Re: 2016 Backfire when up-shifting using shift assist

[Kim_Y]

Hello,


I own a 2016Rt and when I up-shift using the shift assist, I can hear a "pop" in the exhaust, sounds like a backfire. I'm the second owner & this has been the case since I've owned the bike for over a year now.  I just completed the 12k service, checked the cam timing and the cams we're perfectly aligned on both cylinders.  Any suggestions as to what maybe causing this?


Thank you in advance for your assistance. 

[David.]

Just a thought, is it possible that during the up-shift (with shift assist),  the throttle it kept open and the ignition is momentarily cut, causing unburnt fuel to ignite in the exhaust system.

[Graham88]

I am not sure whether BMW quickshifters cut the spark or the fuel injection... if they cut the spark then I would expect to hear that a lot more but I haven't heard it at all.

Does this only happen in certain gears or at certain RPMs or across the range?

[David.]

This video suggests that the ignition is cut, https://www.youtube.com/watch?v=de-lIXeUqYA

The "software" on the bike might need looking at.

[Graham88]

I have seen some conflicting information but fuel modulation is the most logical option, but if that is the case I don't understand why you would get unburnt fuel in the exhaust...

[David.]

This article suggests that on K and S series bikes, the fuel supply is cut, http://www.gelandestrasse.co.uk/2014/04 ... n-bmw.html

It doesn't say what happens on the R series bikes.

[Graham88]

I have not seen a reliable source yet for the exact mode of operation, TMF on youtube is anything but technical. On older machines it was always the ignition to be cut because selectivley controlling a carb for a tenth of second was not feasible but since FI and ECU's made an appearance it became much easier to control with a bit of code.

[David.]

This RT backfires under acceleration too, https://www.youtube.com/watch?v=rT-VdztqN3U

But the fuel is cut when upshifting with GSAP as per this further article, http://www.gelandestrasse.co.uk/2014/11 ... sters.html

"The engine management cuts fuel flow during deceleration, but starts injecting fuel again in preparation for idle as the revs drop below approximately 2,250rpm. You can hear this on the bike as 1–2 slight pops from the exhaust."

Perhaps too much is being expected of the ECU and slight mis-fires are to be expected.

[Kim_Y]

I appreciate all of the feedback.  This mostly happens between 2nd & 3rd gear upshifts, especially loud if I'm hard on the throttle, never when I use the clutch.  David commented it maybe a software issue, which makes sense. Since I've checked the mechanical items already.  The pop would be fuel in the exhaust being ignited.


There were no error codes when I've attached the GS-911, so this was not helpful.  I may need to make a trip to the dealer and see what their diagnostics may reveal. 

[Bakumackem]

It maybe worrying from a mechanical integrity perspective but does it sound good  8)