Stutter when cruising

gmagnus7 · 09-08-2019, 07:17 PM

Hey guys,

I've started to notice a slight stutter or jerking on the highway in 6th gear. It occurs when i'm using cruise control, on flat areas with no change in throttle input. It feels like the throttle is getting cut for a millisecond, or the clutch is slipping but the rpms drop rather than increase. I've attached the logs, you can see the drop in rpm and sometimes ignition timing drops too.

Maybe its a bad injector but it why would that make the rpm drop? I can also hear a a slight clunking sound when it occurs sometimes, and I think it's from the DMFW (it's been slightly audible since switching to the UCC blacks). Maybe the clutch is slipping and/or the DMFW is shot and causing weird vibrations that the knock sensors are picking up?

Not sure what the cause is, lemme know what you guys think. WOT and part throttle are fine and those logs look okay. Whatever it is, it's not kicking it out of cruise when it occurs, and is giving no codes.

EDIT: uploaded zip with 2 logs of it

JimD · 09-26-2019, 07:42 AM

I didn't look at your files but your description rules out the clutch. A clutch that is worn out shows up by slipping when you are accelerating hard and you know it is slipping because the engine rpm increases too fast for the car's rate of acceleration. It wouldn't slip at a steady cruise and then hold during hard acceleration.

I think you need to consider ignition in addition to injectors. Could be a bad plug, coil, or injector.

chris_flies · 09-26-2019, 06:27 PM

I would concur with the above. Possibly a leaking injector.

I'd check both the battery positive cable in the engine bay and the ground strap. Those tend to cause odd little running issues.

gmagnus7 · 10-08-2019, 07:57 PM

Definitely could be fueling related. It does have 4 index 9's and 2 index 12's from when IU originally bought it (and yes I know each bank should have all the same). Switching them all out for all new index 12's in the spring.

I originally thought it was the injectors too but I figured I'd see something abnormal in WOT logs if that's the case. Also was thinking it could be some weird malfunction of the throttle body itself glitching out when in cruise. I'll report back in the spring after I switch out the injectors, going in winter storage for now.

09-26-2019, 07:42 AM	#2
JimD Brigadier General 368 Rep 3,547 Posts Drives: 128i convertible Join Date: Apr 2009 Location: Lexington, SC iTrader: (0)	I didn't look at your files but your description rules out the clutch. A clutch that is worn out shows up by slipping when you are accelerating hard and you know it is slipping because the engine rpm increases too fast for the car's rate of acceleration. It wouldn't slip at a steady cruise and then hold during hard acceleration. I think you need to consider ignition in addition to injectors. Could be a bad plug, coil, or injector. __________________ 128i Convertible, MT, Alpine White, Black Top, Taupe Leatherette, Walnut, Sport Ordered 5/22/09, Completed 6/4/09, At Port 6/9/09, On the Georgia Highway 6/13/09, Ship Arrived Charleston 6/24/09 at 10pm, PCD 7/21/09
	Appreciate 0 Quote

09-26-2019, 06:27 PM	#3
chris_flies Sideways and Smiling 3027 Rep 2,860 Posts Drives: In Exuberance Join Date: Mar 2017 Location: Rosamond, CA USA iTrader: (0) Garage List 2012 BMW E91 328i [0.00]	I would concur with the above. Possibly a leaking injector. I'd check both the battery positive cable in the engine bay and the ground strap. Those tend to cause odd little running issues. __________________ 2012 BMW 328i 6-Speed Wagon \| Deep Sea Blue with Grey Dakota Leather \| Manual Swap, 330i Intake + Tune, 3.15 Helical LSD, Öhlins R&T (SOLD) 2009 BMW 128i 6-Speed Coupé \| Monaco Blue with Black Sensatec \| chris_flies' 128i thread
	Appreciate 0 Quote

10-08-2019, 07:57 PM	#4
gmagnus7 Private 24 Rep 64 Posts Drives: BMW 135i FBO N54 MT Join Date: Mar 2018 Location: Ontario iTrader: (0)	Definitely could be fueling related. It does have 4 index 9's and 2 index 12's from when IU originally bought it (and yes I know each bank should have all the same). Switching them all out for all new index 12's in the spring. I originally thought it was the injectors too but I figured I'd see something abnormal in WOT logs if that's the case. Also was thinking it could be some weird malfunction of the throttle body itself glitching out when in cruise. I'll report back in the spring after I switch out the injectors, going in winter storage for now.
	Appreciate 0 Quote