N55 occasional stumbling on hard acceleration

Ohio Enthusiast · 10-16-2024, 07:14 AM

My 2011 E93 335i automatic with N55 has around 46,000 miles. Previous owner installed a JB4 tune box, otherwise the car is stock AFAICT. When running with the map 1 tune, I noticed that occasionally the car would stumble/hesitate when accelerating hard from a stop. It happens around the 1st to 2nd shift, around 30-40 MPH.

The stumbling typically feels like traction control is kicking in, cutting power for a second and then back on the power. But there is no traction control light on the dash and the roads are dry.
Yesterday, however, it felt like the transmission fumbled the 1->2 shift, as if it switched to neutral for a second and then dropped the clutch, so I'm not sure if the issue is in the engine or the transmission now.

There are no warning lights and no codes, and the car drives perfectly fine otherwise. This happens only rarely, maybe once in 20-30 hard accelerations.

I changed the JB4 tune to map 0 (no tune) today, and will see if this happens again in the next few days/weeks.

I have a THOR OBD adapter, is there a way to log something to get more insight into this issue since it's hard to reproduce?

Ohio Enthusiast · 10-16-2024, 12:28 PM

Well, looks like it happened with the map 0 tune, but this time it did flash the traction control light. It felt mostly the same as previous times, so I guess it's just traction control and I missed the light previous times. I'll give a few more times with map 0, and then try with DTC on to confirm that this is indeed just the traction control. Luckily JB4 has an option to automatically "press" the DTC button, so I wouldn't need to remember to push it every drive.

10-16-2024, 07:14 AM	#1
Ohio Enthusiast Private 68 Rep 63 Posts Drives: '11 E93 335i, '18 BRZ Join Date: May 2024 Location: Dayton, OH iTrader: (0)	N55 occasional stumbling on hard acceleration My 2011 E93 335i automatic with N55 has around 46,000 miles. Previous owner installed a JB4 tune box, otherwise the car is stock AFAICT. When running with the map 1 tune, I noticed that occasionally the car would stumble/hesitate when accelerating hard from a stop. It happens around the 1st to 2nd shift, around 30-40 MPH. The stumbling typically feels like traction control is kicking in, cutting power for a second and then back on the power. But there is no traction control light on the dash and the roads are dry. Yesterday, however, it felt like the transmission fumbled the 1->2 shift, as if it switched to neutral for a second and then dropped the clutch, so I'm not sure if the issue is in the engine or the transmission now. There are no warning lights and no codes, and the car drives perfectly fine otherwise. This happens only rarely, maybe once in 20-30 hard accelerations. I changed the JB4 tune to map 0 (no tune) today, and will see if this happens again in the next few days/weeks. I have a THOR OBD adapter, is there a way to log something to get more insight into this issue since it's hard to reproduce?
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10-16-2024, 12:28 PM	#2
Ohio Enthusiast Private 68 Rep 63 Posts Drives: '11 E93 335i, '18 BRZ Join Date: May 2024 Location: Dayton, OH iTrader: (0)	Well, looks like it happened with the map 0 tune, but this time it did flash the traction control light. It felt mostly the same as previous times, so I guess it's just traction control and I missed the light previous times. I'll give a few more times with map 0, and then try with DTC on to confirm that this is indeed just the traction control. Luckily JB4 has an option to automatically "press" the DTC button, so I wouldn't need to remember to push it every drive.
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