M-DCT Lag - What's the reason?

[footie]

Originally Posted by swamp2

3. The lag is mostly eliminated by using S modes. What is the actual difference in what is happening under such use - SOFTWARE. The behavior of the hardware can absolutely, in principal, be duplicated from S mode in D mode through software.

I find that regardless of whether or not you are either D or S mode, if you let the gearbox choice the point of when to shift down you can experience and duplicate the lag.

Originally Posted by swamp2

4. As was pointed out other cars such as the Ferrari California use this hardware. I've heard nothing of such a lag in reviews of the car.

I remember saying a while ago that I felt it may be a engine ECU + gearbox software problem and the very fact that the Ferrari is problem free only strengthen my belief in this opinion.

Originally Posted by swamp2

5. I refuse to believe the transmission could have made it through early development with such a flaw.
6. Other DCT transmissions do not show a similar flaw. If it were so difficult to get around this problem others would likely show the same flaw.

The essence of a DCT transmission is its software. And although there is clearly no AI type software being used, the software is complex and does closely communicate with other complex - the ECU software.

Call me overly optimistic if you like. Sure, as an owner of this tranny, I do hope there is no such critical hardware flaw. However, my reasoning above is not thrown together from desperation, it is sound and logical. I don't see any real evidence that it is such a critical hardware flaw. Part of the reason is that the claim is so highly speculative. It almost requires detailed knowledge of the design and dynamics of the internals, which for all practical purposes, none of us will ever have.

Here is where you and I differ greatly swamp. You seem to be convinced that the almighty M-Division couldn't possibly release something with problems just to say they were first with a DCT that wasn't transverse, where as I am convinced that they have exactly done this very thing feeling that they were close enough to having a fix that this could have been sorted shortly after those early examples were sent to their owners. But this hasn't proven to be the case and now after almost a year there is a shit load of customers that are very unhappy with how this issue has been dealt with, and rightly so.

I'm still of the opinion that either it's the gearbox or engine software but something in this combination that is self learning because I definitely had zero lag after the car was left into the dealer last time for all of 2 1/2 weeks and if it didn't learn then this shouldn't have been the case and nothing should have changed.

I am also convinced that they will eventually fix it's problems but the very fact that they were there and is taking so long to fix lessens the high opinion I had for BMW and their M-Division.

[swamp2]

Originally Posted by footie

I find that regardless of whether or not you are either D or S mode, if you let the gearbox choice the point of when to shift down you can experience and duplicate the lag.

I did not say S eliminates lag but I do find it improved.

Originally Posted by footie

I remember saying a while ago that I felt it may be a engine ECU + gearbox software problem and the very fact that the Ferrari is problem free only strengthen my belief in this opinion.

I have been saying 100% software and also ECU and TCU for some time. On the other hand you have, even very recently, and right here in this thread, been in the critical hardware flaw camp, which with the drive report above seems almost for sure incorrect.

Originally Posted by footie

Here is where you and I differ greatly swamp. You seem to be convinced that the almighty M-Division couldn't possibly release something with problems just to say they were first with a DCT that wasn't transverse, where as I am convinced that they have exactly done this very thing feeling that they were close enough to having a fix that this could have been sorted shortly after those early examples were sent to their owners. But this hasn't proven to be the case and now after almost a year there is a shit load of customers that are very unhappy with how this issue has been dealt with, and rightly so.

We don't differ. For me to disagree with that would be to disagree with known facts. Quite frankly I do think this bug is a bit unbecoming and yes even a bit "below" the M division. But disagreeing with clear facts in evidence, no I don't do that. Obviously I too am also unhappy with how this has played out.

[footie]

I can't remember which UK magazine ran a group test that included the new Z4 35i with DCT but their comments of the latest version of the BMW DCT got very high praise indeed. They remarked that it was better than the PDK from Porsche and in their opinion was the best DCT currently available.

Great news for Z4 owners but bad news for us, their commented that in their opinion the M3 offered too many settings with the DCT (nothing new there) reckoning that auto and sport were all that was needed but were as the M3 suffers lag contiuously the Z4 suffers none.

This begs the question as to what makes the Z4 and it's 35i engine combination different to that of the M3?

[BarryC]

Originally Posted by mkoesel

Interesting info - thanks for posting. I do recall now that the California was one other car that used this transmission. Too bad we can't just get the Ferrari software. Heh heh kidding of course, I am sure that the controller is completely different. But maybe the third party software swamp pointed out awhile back will be here soon.

BTW, how'd you get a drive in that car? Very lustworthy car.

I'm a lucky boy! Actually the local Ferrari/Porsche dealer has a demo and a salesman friend of mine let me drive it. First time in a Ferrari and must say I would give my left nut for the California! I told my wife that maybe we could sell my car and her Cayenne to raise enough $ for a downpayment! She actually considered it for a second or two. Maybe someday.....

BC

[SenorFunkyPants]

Having been in contact with Getrag (the DCTs manufacturer) about a different matter I've now asked them about this issue and included a link to this thread. It will be interesting to see what (if any) response I get.

[Gearhead999s]

[QUOTE=

This begs the question as to what makes the Z4 and it's 35i engine combination different to that of the M3?[/QUOTE]

Torque!I am always amazed when I drive my wifes 335/auto and how well that combination works.

[swamp2]

Originally Posted by SenorFunkyPants

Having been in contact with Getrag (the DCTs manufacturer) about a different matter I've now asked them about this issue and included a link to this thread. It will be interesting to see what (if any) response I get.

Good idea I would love to hear from Getrag. However, on issues such as major vehicle components sourced from suppliers, it seems the manufacturers try to keep in on the DL as to who is their supplier and basically take credit for the component. I don't mean BMW has totally hidden their DCT supplier, but I suspect all comments, if any, just like the repairs, warranties and recalls will be the exclusive domain of BMW, not Getrag.

[shchow]

Stupid question...I thought the DCT has rev-matched downshifts (heel-toeing without the heel and toe)?
If so, why would there be a lag?

[Projectile]

Originally Posted by shchow

Stupid question...I thought the DCT has rev-matched downshifts (heel-toeing without the heel and toe)?
If so, why would there be a lag?

I'm speculating, but My guess is that while decelerating, the computer suspects you are going to stop and to prevent stalling, it does the same thing you would do if you put your foot on the clutch while decelerating to prevent a stall. Then, the lag comes in because when you press on the accelerator wanting to get going again, the computer realizes you are NOT decelerating to a stop anymore and it takes a second or 2 to do whatever the DCT equivalent is of selecting the appropriate gear and letting the clutch out with some throttle to get going again.

If that is the case, it does sound like normal behavior to me, and one that might be hard to solve. VW and Audi drivers have complained of similar lag issues, so that's partly why I suspect that it is inherent to this type of transmission. Perhaps a downshift into 1st gear is what it ought to be doing. Presumably, manually downshifting into first gear ought to solve it if that's the problem, though at some point, again, if you keep decelerating, you are going to end up, even in first gear, at a speed that might cause a stall if DCT doesn't do the equivalent of depressing the clutch, and you're back in the same loop.

The explanation I have provided above (again - pure speculation, though it makes sense to me) would also fit with the observation that the lag problem became evident after a software upgrade to prevent stalling.

P

[swamp2]

Originally Posted by Projectile

I'm speculating, but My guess is that while decelerating, the computer suspects you are going to stop and to prevent stalling, it does the same thing you would do if you put your foot on the clutch while decelerating to prevent a stall.
...

Fairly poor speculation. Read the thread. The Ferrari California has the same transmission and does not exhibit this behavior. Furthermore, the time to clutch and shift the DCT can be as little as 10's of miliseconds. There is no essential reason for this lag. It is a bug, pure and simple. Now that being said it does seems to be quite difficult for BMW to fix given the multiple software versions there have been.

[footie]

Originally Posted by swamp2

Fairly poor speculation. Read the thread. The Ferrari California has the same transmission and does not exhibit this behavior. Furthermore, the time to clutch and shift the DCT can be as little as 10's of miliseconds. There is no essential reason for this lag. It is a bug, pure and simple. Now that being said it does seems to be quite difficult for BMW to fix given the multiple software versions there have been.

It's in the California and the new Z4 3.5i and in both there appears to be no problems what so ever. So I can only conclude that the problem lays with the DCT + N65 combination, i.e. both gearbox software and engine ECU are not great bed fellows.

I don't agree that the delay has anything to do with the multiple software versions there has been, each upgrade supercedes the last one and once your car is updated the old version is wiped clean.

I believe this isn't high up in BMW's priority list at the moment, or not high enough to place the same man hours that a life or death issue would do. So until someone actually dies (heaven forbid) as a result of the lag I think we will be put on the long finger.

Please prove me wrong Mr BMW, I dare you.

[mkoesel]

Originally Posted by footie

It's in the California and the new Z4 3.5i and in both there appears to be no problems what so ever. So I can only conclude that the problem lays with the DCT + N65 combination, i.e. both gearbox software and engine ECU are not great bed fellows.

Just one note footie - it is also in the 335i and there the lag is present also so whatever the cause it appears to inflict both the S65 and N54 ECU as it exists in these cars. The Z4 35i case definitely gives us hope this can be solved, however there is still no guarantee it can be fixed in software alone.

(BTW, no N65 exists - though 3 and 5 series owners may wish it did But I knew what you meant.)

[aus]

Originally Posted by mkoesel

Just one note footie - it is also in the 335i and there the lag is present also so whatever the cause it appears to inflict both the S65 and N54 ECU as it exists in these cars. The Z4 35i case definitely gives us hope this can be solved, however there is still no guarantee it can be fixed in software alone.

(BTW, no N65 exists - though 3 and 5 series owners may wish it did But I knew what you meant.)

The lag for the N54 was due to BMW keeping the bypass valves open because they were rattling on some cars. It was a software fix for a mechanical problem. It was cheaper than than changing out all the valves.

Originally Posted by D-Rock

Seems like 6 speed is the way to go

Originally Posted by swamp2

Not sure how many times this needs to be repeated. Despite this fairly large bug most owners would still choose DCT over MT. First you can drive round it, second it is only at low speeds and during mellow driving and lastly there is likely to be a fix for it. I still rate the tranny 9.5/10.

Don't respond to the trolls.

Originally Posted by swamp2

It is a point worth giving a +1 to. Although I have not found time to get my car on the track I have tore up some great So Cal desert and mountain back roads and the tranny is flawless. I'd be willing to bet this lag NEVER showed up in your track work right? This certainly is not a justification, excuse nor reason the issues should be ignored just to reiterate this small flaw doesn't ruin the DCT experience.

No issues with DCT for me either.

[mkoesel]

Originally Posted by aus

The lag for the N54 was due to BMW keeping the bypass valves open because they were rattling on some cars. It was a software fix for a mechanical problem. It was cheaper than than changing out all the valves.

That's not the lag I was talking about though. I was talking about the same lag that the M-DCT exhibits. The 335i with DCT also has this lag.

[Locksmythe]

I am new to this board, as I just traded in my 550i for my DCT e92, so forgive me if I incite violence with this post. I read reviews of the double clutch transmissions (other makes/models) before considering the M3 and it was a not uncommon point mentioned in the reviews that there would be a delay in shift if the driver drove unpredictably, as the marvelous .1 second shifts depended on the computer being able to anticipate the next required gear and preloading it on the disengaged clutch. I have only read about a third of the angry posts here, but those that do describe their lag have all described situations in which they are obviously making unpredictable (from computer perspective) speed changes. It's not like the car can look ahead at traffic and decide that you are waiting for an opening, or that you are going to try to change lanes aggressively from a casual pace, or that you will reaccelerate suddenly after dropping throttle altogether, or that today you happen to be driving nice and gentle because you have guests in the car but you have not changed your shift program. The clutch is taking a guess at what you are doing and you are giving it all the wrong clues.

I understand that you believe a particular software update caused all of this (at the time it fixed stalls), and I too believe that a software change could indeed improve upon this problem. I also believe that such a change would have an adverse effect on the other 95% of the time the car shifts in predictable ways. No matter what they do, the two clutches and gear sets will not be able to switch from that anticipated next gear to an unanticipated one any faster than it takes to move the mechanisms. It will never be as fast as an anticipated shift.

The one thing I think I would want added is a visible indicator that the clutch is engaged. If only I knew when I was allowed to go full throttle... Or that the car would not roll into a curb as soon as i release the parking brake and lift my foot onto the accelerator... I have heel toed out of more parking places in the last week than I have during a downshift in my life.

I am curious, how many of the people with this problem have experience with technical development or engineering? Are there software coders having this problem? It's a mindset question, so try not to get offended.

[chris719]

I'm pretty sure that if this was a purely software issue it would have been solved completely by now and the fix forced on everyone.

[mkoesel]

Originally Posted by chris719

I'm pretty sure that if this was a purely software issue it would have been solved completely by now and the fix forced on everyone.

You've a bit late - we've already had that debate.

[swamp2]

Originally Posted by Locksmythe

I am new to this board, as I just traded in my 550i for my DCT e92, so forgive me if I incite violence with this post.
...

There is no way you are going to incite violence. However, if you want to be informed and speak intelligently on this topic you should read the entire thread. We know this is a software problem and we know it can be fixed 100% with no adverse affects on upshifting or other aspects of the performance of the system.

By the way, since you asked, my background is math, physics and mechanical engineering. I've done some programming as well. There are a lot of scientists, engineers and programmers here on this forum.

[nitramsen]

Originally Posted by swamp2

There is no way you are going to incite violence. However, if you want to be informed and speak intelligently on this topic you should read the entire thread. We know this is a software problem and we know it can be fixed 100% with no adverse affects on upshifting or other aspects of the performance of the system.

By the way, since you asked, my background is math, physics and mechanical engineering. I've done some programming as well. There are a lot of scientists, engineers and programmers here on this forum.

How can you be sure that this is a 100% software error?

If you ask me there is more and more that points in the direction of some kind of mechanical issue ( Maybe pneumatically). If you have update > 33 then you will realize why I think this could be a possibility.

Why would BMW deny a fixable software bug and why would it take so long time to be fixed as this could easily be simulated?

Have you ever tried reading the CAN or OBDII during a lag attack?

And for those who do not have 33 or above it is worth getting it, but does not solve the lag 100%

[swamp2]

Originally Posted by nitramsen

How can you be sure that this is a 100% software error?

There are other cars with identical hardware with no lag.

[aus]

Originally Posted by nitramsen

How can you be sure that this is a 100% software error?

Because this issue wasn't there before the SOFTWARE update to fix other issues with the tranny was done.

[nitramsen]

Originally Posted by aus

Because this issue wasn't there before the SOFTWARE update to fix other issues with the tranny was done.

Exactly my point for a mechanical issue. Why would they introduce a lag via software if this is not a physical related phenomen?

You are talking about a COMPANY with massive processing power in both human and hardware form so if this was a pure software bug this would have been solved long ago. I assume BMW knows about regression test and therefore this points in my direction not your.

And to Swamp2 I have read the thread and I see no proof of pre March 2009 DCT working. I assume that if BMW realizes that they made a mechanical mistake they will try to fix it in later versions. Like they have done in all previous M's with mechanical issues where they fix it but did not provide early version with any corrections.(I still remember the high oil burn of early E39 m5 compared to after 2001, did BMW provide a fix for pre 2001?)

But how many of you have actually tried to trace the error via OBDII or CAN?
I assume few so why don't you Swamp2 use your Math,Physics with limited development exprience to tried to get some hard facts for your postulates.