[f3003f]

hi all! please help me diagnose the issue.

I was in neutral when I merged from one freeway to another. Once I was on the new freeway I was going 30-35 mph, I revved up to 3-4k RPM and put the car in 3rd gear and floored it. While maintaining full throttle (and not touching the clutch) the car accelerated smoothly to little less than 6k RPM then the RPMs when down to 5.5k RPM and bounced around there (5.5 - 5.7k RPM) that continued for few seconds and then RPMs dropped to 4k RPM. I was really confused, but kept full throttle for few seconds. The car was not accelerating and RPMs stayed at 4K. Then I put it neutral for a second then 4th gear and everything was back to normal. After I stopped I could smell a burning smell coming from the front of the car. I tried accelerating quickly in 3rd again and that time everything was fine. What do you think is going on?

This is actually the second time this happens. The first time it happened about a year ago under the same circumstances. I went to the dealership then, but they didn't find anything wrong (they didn't open the clutch, the shop foreman drove with me to test it).

Thank you in advance!

[Billfitz]

To check if the clutch is OK drive at 30-35MPH, put the car in top gear, and floor it. If the engine races then the clutch is worn.

[mark1996]

Sounds like an engine problem rather than a clutch problem. If your clutch is worn or slipping, you will see and feel your RPM's rising without the car's speed increasing.

My guess based on your symptoms would be a faulty traction control system. This system will back off on the RPM's if the sensors are telling it, correctly or incorrectly, that a driven wheel is losing traction.

[S4NoMore]

Why are you in neutral at speed? That is not a good practice, you should break the habit. There's no reason to coast in neutral, especially in a merge situation. If you needed to accelerate for any reason you'd be at risk as you fumble to get in gear.

When the engine dropped to 5.5-5.7k and then to 4k, did the car slow and get jerky - i.e. did your speed fluctuate accordingly? I'm guessing that it did.

As others have said, a clutch issue will result in engine speed fluctuations independent of vehicle speed. If the whole car is slowing down, hesitating, not accelerating, then it's an engine problem. Could be traction control, could be misfires. Did you not get any check or warning lights? Did you recently fill up your tank, what fuel do you run?

[Thumper333]

Originally Posted by S4NoMore

Why are you in neutral at speed? That is not a good practice, you should break the habit. There's no reason to coast in neutral, especially in a merge situation. If you needed to accelerate for any reason you'd be at risk as you fumble to get in gear.

+1

Need to practice heal-toe rev matched downshifts and keep control of the car at all times. Coasting has you out of control of the car.

A worn clutch will not limit RPMs, the fact that it stuck at 4k RPMS leans me to thinking it went into limp mode, especially if the engine was 'bouncing' revs, sounds like rev limiter.

No engine lights or anything on the dash? The suggestion of traction control seems like a good first attempt outside of any warning lights. Although the traction control light should have illuminated if the system was active, maybe you just didn't notice it.

Either way, another trip to the dealer seems prudent.

[f3003f]

Billfitz thanks for the advice, I'll try that and post the result!

mark1996 thanks! That makes sense. Would a faulty traction control system explain the burning smell? I can still smell today about 18 hours later, it's less noticeable, but still there.

S4NoMore The merge was a single lane that loops on the freeway below and then has a dedicated lane, so had plenty of time to shift back into gear, but thanks for the concern! As far as I remember (it all happened within 5-7 seconds) the speed didn't not fluctuate, it remained relatively the same, maybe was slowing down like I was in a gear and not pressing gas. There were no warning lights. I've been only using Shell 91 and had a little less than 3/4 full.

Thumper333 correct, didn't see the traction control light come on. It's near the tachometer, so I think I would have noticed it. Thanks! I've made an appointment for next week.

Thanks all for suggestions

[BavarianFanatic]

I think the primary problem is that you don't have an automatic...

[f3003f]

BavarianFanatic do you think the warranty will cover that?

[mark1996]

Burnt smell? Rear brake pads? I am not 100% sure about the F30 but on other BMW models the traction control activates the rear brakes to control wheel spin.

[f3003f]

mark1996 that's interesting. The smell was definitely coming from the front or at least the majority of it. Thanks for the reply!

[f3003f]

Looks like the clutch is fine!

As suggested by Billfitz I put in 6th gear 35mph and floored, it was slow but steadily (without any slippage) accelerated. I've tried this multiple times, each time everything went fine. I also tried reproducing the problem by doing almost exactly what I did yesterday, but this time there were no issues.

The smell is still there, however, it's faint now (over 24 hours later) and all in the front (right by the driver's door).

[Thumper333]

Originally Posted by f3003f

The smell is still there, however, it's faint now (over 24 hours later) and all in the front (right by the driver's door).

Check the fuse box? LOL

I dunno, very weird one, interested to see what they eventually find.

[rking117]

if you didn't have your foot on the brake and you had a burning smell under acceleration then it is clutch for sure. that however would not mean your clutch is worn out. do you think your foot could have engaged the clutch and not know it. I have at times rested my foot a little to hard had caused that to happen. I try not to rest my foot on that pedal if i can help it though. Power shifting is my friend.

[f3003f]

rking117 as far as I remember, I had my foot off the clutch.

I took a test drive with a foreman at a local dealership he said the club was good, but was releasing late and there was some shudder. They are taking a look today. He said it sounds like the clutch could have overheated and caused that weird RPM bounce, but I'm not sure if that could be it, since I was just cruising on the freeway the time before this happened.

[RPM90]

Originally Posted by f3003f

rking117 as far as I remember, I had my foot off the clutch.

I took a test drive with a foreman at a local dealership he said the club was good, but was releasing late and there was some shudder. They are taking a look today. He said it sounds like the clutch could have overheated and caused that weird RPM bounce, but I'm not sure if that could be it, since I was just cruising on the freeway the time before this happened.

Could be a glazed clutch.
You'll get some shudder mostly on take off with slower clutch pedal release.
It's friction material build up on the flywheel, and some transferred back unevenly onto the clutch.
It can happen when on does what you described.
High torque along with clutch perhaps not engaged quickly enough.

One way to try an get rid of it is to drive normally with no heavy accel for a while. Normally it smooths itself out.
Some drive off in 2nd gear can help too, just don't use big rpm and don't let the clutch pedal out too slowly. You want the clutch to grab quickly. It will help rub off/smooth out the glazed material.

[f3003f]

RPM90 yes, that's exactly what was happening. The service advisor said she will know more tomorrow on what happened with the clutch.

I'm now mostly concerned with why the RPMs got stuck at 4k. As others have posted that could be from traction control, does that mean some sensor is not working properly?

Thanks for the reply!

[RPM90]

Originally Posted by f3003f

RPM90 yes, that's exactly what was happening. The service advisor said she will know more tomorrow on what happened with the clutch.

I'm now mostly concerned with why the RPMs got stuck at 4k. As others have posted that could be from traction control, does that mean some sensor is not working properly?

Thanks for the reply!

I wouldn't think so with what you described.
What others could have been talking about is that when the car is in default traction mode then if the rear drive wheels spin the computer will sense that and to control the wheel spin with take over throttle control by lessening throttle even though your foot may be well planted.

The computer can use both throttle control and braking to bring traction back under control.
With straight line accel it's mostly throttle. On big curves if the rear starts to slide the system can control both brake and throttle to bring the car back in line.

In your situation the cars mass was already moving, you de-clutched, applied big engine rev, and then either dumped or applied the clutch.
As the car was already in motion as soon as the clutch grabs the flywheel there is going to be forcefull meeting of the 2 surfaces, heat and pressure.
AS you kept on the throttle at that rpm the meaty part of the torque band is also right there. Depending on how you applied the clutch there could have been an initial grab followed by acceleration until the big torque came on causing the slip, grab, slip, grab. I can see how the rpm could hang during this with just the clutch grabbing and slipping.

Throw in traction control and that's another element.
In the scenario it could be that you glazed the clutch on initial rev and dump, and once the clutch grabbed and peak torque started pulling, traction could have broken loose, which would get the computer to take control of engine rpm.

The main thing at this point is to get the clutch sorted.
If you do a clutch dump again, remember to try and match the engine revs based on vehicle speed, the gear you want, and where that will land you on the tach/engine speed. You want to try and match that up as best as you can so that when the clutch bites it's not going bog/drag down the engine (gear too high), nor accelerate the engine too much and too quickly (gear too low).

Do some testing and figure out what gear give you what rpm at the same given vehicle speed. In short order you'll start to know what gear you need and how to apply it depending on how fat you're moving. It's part of the fun of enjoying a manual trans.