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      03-02-2012, 06:49 PM   #1
Gnip Gnop
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DCT...DTC power loss??

So I was driving home from work today and noticed something unusual.

I have an n55 dct (7 speed) and I was in m5, and had sport mode on.

I gave it a small bit of throttle, and hit the DTC button, and I experienced a loss of power. It felt exactly what it would feel like if you turned sport mode off. The throttle response was reduced greatly compared to what it was before. Then I gave it the same amount of throttle while having DTC ENGAGED, turned DTC off, and I gained my power/throttle response back.

So does having DTC engaged, or everything completly off did it as well, reduce power output?
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      03-02-2012, 07:08 PM   #2
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My guess would be doing all of that at the same time caused the system to "hiccup" perhaps.

Does it do it every time under the same circumstances? Maybe it's one of those things where the patient says, "doctor, it hurts when I do this;" and the doctor says, "well, then don't do that."
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      03-02-2012, 08:16 PM   #3
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Quote:
Originally Posted by BimmerEnthusiast99 View Post
My guess would be doing all of that at the same time caused the system to "hiccup" perhaps.

Does it do it every time under the same circumstances? Maybe it's one of those things where the patient says, "doctor, it hurts when I do this;" and the doctor says, "well, then don't do that."
I have never noticed it, because whenever I hit dtc, I am at a stop. So I guess the only reason I noticed is because the car was in boost. I even heard the turbo push less psi.
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      03-03-2012, 02:05 AM   #4
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Can anyone else help out on this issue? Anyone experience something similar?
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      03-04-2012, 01:14 PM   #5
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I actually think it's normal. I don't know for sure but I have a suspicion that BMW tunes the sport mode with DTC on to be more aggressive than with it off precisely because it's so easy to lose traction.

For the record, I actually noticed this exact same behaviour in my car in the last couple of weeks, but like you I never really thought about it before because I don't remember ever turning DTC off while actually driving.

I will note that out of curiosity I tried on a straight empty stretch of road accelerating to 40mph, holding the throttle and then trying DTC on/off and sport mode on/off. The sport mode off definitely made much more of a difference than the DTC off, but yes there's a definite feeling of less throttle response. Try turning DTC off and then sport mode off and you'll notice a "two step" feeling.

I have a feeling that because the DCT has a shorter geared rear than the 6MT it's probably far too easy to break traction under hard acceleration in the DCT than the 6MT. BMW probably made the choice to slightly detune the throttle response so that you'll actually still be able to control it properly instead of turning your expensive RFT's into foul smelling smoke.
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      03-04-2012, 04:19 PM   #6
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Quote:
Originally Posted by Sinister Crayon View Post
I actually think it's normal. I don't know for sure but I have a suspicion that BMW tunes the sport mode with DTC on to be more aggressive than with it off precisely because it's so easy to lose traction.

For the record, I actually noticed this exact same behaviour in my car in the last couple of weeks, but like you I never really thought about it before because I don't remember ever turning DTC off while actually driving.

I will note that out of curiosity I tried on a straight empty stretch of road accelerating to 40mph, holding the throttle and then trying DTC on/off and sport mode on/off. The sport mode off definitely made much more of a difference than the DTC off, but yes there's a definite feeling of less throttle response. Try turning DTC off and then sport mode off and you'll notice a "two step" feeling.

I have a feeling that because the DCT has a shorter geared rear than the 6MT it's probably far too easy to break traction under hard acceleration in the DCT than the 6MT. BMW probably made the choice to slightly detune the throttle response so that you'll actually still be able to control it properly instead of turning your expensive RFT's into foul smelling smoke.
Thanks for the great response. That makes sense, I'm glad to hear its not only my car having this issue.
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