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      06-02-2014, 08:44 AM   #1
CarAbuser
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Couple of Questions (DCT & Engine)

Hi,

Couple of questions that have been on my mind for a while now;

1. How does the DCT handle being stationary while in D?

Does it slip the clutch while sat in 1st gear with the brake pedal held? Even a slight release from the brake pedal will cause it to creep forward so I get the impression it's just sat slipping!

2. Engine Vibrations

I had my HPFP replaced under warranty at 28,000 miles. Since having it replaced I have been paying a lot more attention to the engine. It seems to have a slight shudder while idling. It's only very slight and there are no fault codes active (scanned with BMWhat app).

The revs do not fluctuate when the shudders happen but they are fairly frequent (every two seconds). I was thinking it could possibly be the injectors or coil packs as they are something which others have frequently had changed via warranty but with no error codes active I doubt the garage would care.
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      06-02-2014, 09:26 AM   #2
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Quote:
Originally Posted by CarAbuser View Post
Hi,

Couple of questions that have been on my mind for a while now;

1. How does the DCT handle being stationary while in D?

Does it slip the clutch while sat in 1st gear with the brake pedal held? Even a slight release from the brake pedal will cause it to creep forward so I get the impression it's just sat slipping!
I've noticed that if you are at a complete stop (in D or any other mode) and take your foot off the brake there is an ever-so-slight decrease in engine RPM (accompanied by a change in sound consistent with a slight load being placed on the engine - similar to an AC compressor turning on at idle). So I believe that at a stop with your foot on the brake the clutch is completely disengaged, but removing your foot from the brake slightly engages the clutch to produce a "creep mode" like that of a torque converter.

It really doesn't make sense to me that the clutch would always be slipping as there's no need for that to be the case, and IF it was the case then I wouldn't see the slight drop in engine RPMs when releasing the brake.

Quote:
2. Engine Vibrations

I had my HPFP replaced under warranty at 28,000 miles. Since having it replaced I have been paying a lot more attention to the engine. It seems to have a slight shudder while idling. It's only very slight and there are no fault codes active (scanned with BMWhat app).

The revs do not fluctuate when the shudders happen but they are fairly frequent (every two seconds). I was thinking it could possibly be the injectors or coil packs as they are something which others have frequently had changed via warranty but with no error codes active I doubt the garage would care.
I don't really have a comment on this as I can't say that I have noticed it save for what I mentioned above - a slight shudder or change in idle RPM or engine load when I take my foot off the brake. But there's at least two other engine-driven systems that could cause a slight shudder at idle (indicating a slight change in engine load) - the AC compressor and the alternator.
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      06-02-2014, 10:12 AM   #3
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Quote:
Originally Posted by JR956678 View Post
I've noticed that if you are at a complete stop (in D or any other mode) and take your foot off the brake there is an ever-so-slight decrease in engine RPM (accompanied by a change in sound consistent with a slight load being placed on the engine - similar to an AC compressor turning on at idle). So I believe that at a stop with your foot on the brake the clutch is completely disengaged, but removing your foot from the brake slightly engages the clutch to produce a "creep mode" like that of a torque converter.

It really doesn't make sense to me that the clutch would always be slipping as there's no need for that to be the case, and IF it was the case then I wouldn't see the slight drop in engine RPMs when releasing the brake.



I don't really have a comment on this as I can't say that I have noticed it save for what I mentioned above - a slight shudder or change in idle RPM or engine load when I take my foot off the brake. But there's at least two other engine-driven systems that could cause a slight shudder at idle (indicating a slight change in engine load) - the AC compressor and the alternator.
Thanks. The disengaging of the clutch makes sense.
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      06-02-2014, 10:18 AM   #4
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I agree on the DCT. The RPM changes depending on whether you fully depress the brake or let off ever so slightly so that the car thinks you are getting ready to move. Slip would happen if you only gently touched the brake just enough to keep the car from moving, but not fully pressed.

Normally I shift into N when I need to stop for more than 10s though... simply because I graduated from the manual transmission school in Europe...

Regarding the shuddering, well assuming that we are experiencing the same, then yes, mine does it very very rarely, and during some trips not at all, but it started after I had my spark plugs changed. Not sure what causes it though...
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      06-02-2014, 12:36 PM   #5
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OP, I think the vibrations when your car is idling is worth looking into. My car was doing that and the injectors needed replacing. There was also a long crank at start that signaled HPFP needing to be replaced at the same time.

There were no trouble codes or check engines light when all these things were replaced.
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      06-02-2014, 01:37 PM   #6
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Quote:
Originally Posted by Asbjorn View Post
Normally I shift into N when I need to stop for more than 10s though... simply because I graduated from the manual transmission school in Europe...
+1, though my school was in the States .
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      06-02-2014, 05:41 PM   #7
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I had plenty of error codes with the HPFP. It was running lean for a while. As soon as I took it into the dealers they replaced it without a word.

I do think there may be a slight issue with either the injectors or coil packs. The judders are only very slight so I'm unsure if they will do it under warranty. I will ask when it goes in for its next service.
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      06-02-2014, 06:30 PM   #8
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In my limited experience, if the fuel pump and injectors are okay, judders and shudders at idle likely indicate a problem with ignition coils or spark plugs. Plus are easier to replace than coils and both are easier than injectors.

Thus, I would probably start with new plugs, then try new coils, and then perhaps injectors. If you have a sophisticated scan tool, you can also see whether any cylinders have reported knock events. If one cylinder is an outlier in that regard, it's probably a bad plug and/or coil on that cylinder. Just dealt with this on the M3 (which has DCT, for what that's worth).
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      06-02-2014, 07:46 PM   #9
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Another thing to check is the fuel trim values. I believe that was what prompted the injector replacement on my car.
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      06-09-2014, 11:54 AM   #10
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Since I just joined the DCT club (from manuals my entire roadster life) I too had a couple questions.

Should the tranny shift seamlessly in regular Drive as a "standard" automatic transmission does? Seems like mine shifts with a little bit of a jolt. Also when first starting in the morning it hesitates for a few seconds before engaging.

Fine with me if this is the way it is supposed to be but thought I'd get some input in case this is not normal so I can take it into the shop while still under warranty.
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      06-10-2014, 01:36 AM   #11
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Mine shifts perfectly in comfort mode. Better than any standard automatic I've driven.
I only know what gear I'm in by checking the display as it shifts seamlessly.

The delay before starting off could be down to software. They added a creep function in later revisions to combat jerky engagement during manoeuvres.
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      06-10-2014, 06:05 AM   #12
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Quote:
Originally Posted by Eltee View Post
Should the tranny shift seamlessly in regular Drive as a "standard" automatic transmission does? Seems like mine shifts with a little bit of a jolt.
My 2014 35is shifts 98% seemlessly in regular drive - at least as long as I am not getting too heavy on the accelerator pedal it's about as smooth as my 2014 X3 with the 8-speed automatic - maybe even smoother. I can hear it shift (based on exhaust note) but I really can't feel it shift.

If I venture away from drive into gearbox sport mode (tilting the transmission control lever to the left) it's very slightly less smooth but does blip the engine on upshifts as well as downshifts. In gearbox sport mode shifts are at a significantly higher RPM. I suspect these blips are done with ignition rather than throttle; regardless they sound pretty cool.

If I also venture away from Comfort mode to Sport mode (via the switches on the center console for Comfort, Sport and Sport+) those upshift blips stop and I get anywhere from a slight jolt to a more significant jolt depending again on what I do with the accelerator pedal.

Quote:
Also when first starting in the morning it hesitates for a few seconds before engaging.
When first starting in the morning the idle RPM is significantly higher than idle after a slight warm-up, and the first engagement (to back out of my garage) requires a bit of throttle before the car moves. This is distinctly different than "creep mode" where simply taking your foot off the brake will start the car moving slowly. Creep mode seems to be disabled until idle speed drops back to normal and that doesn't happen for a minute or so after a cold start.
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      06-10-2014, 11:38 AM   #13
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Thank you for the input. Sounds like a trip to the dealer.
When I was driving home from out east after purchasing the car, I got a "transmission failure" warning. That'll scare the hell out of you when you're out in the middle of nowhere in the hills of West Virginia. Had only even forwards gears and no reverse. Fortunately when I shut the engine down on restart everything was fine. When I got home the dealer said it was just a computer glitch that they corrected but me thinks there is more to it.

Again thanks
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      06-04-2015, 08:03 AM   #14
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One year later and my car was about ready to leave warranty. Went in for a final "free" oil change and asked them to check the above transmission shifting issue that was still bothering me.
They found transmission "functions as designed" (one of my favorite cop out reasons for not fixing something)
On the way home got the infamous "transmission failure" light and limped home.
Brought back to the dealer 2 weeks ago. Got a new 328GT loaner and they have been working on my Z ever since.

Apparently they've put in a couple new modules and have been in conversation with BMW routinely trying to diagnose the problem.

Talked to them a couple days ago and the service rep said they are actively working on it but 2 WEEKS??

Doesn't this seem a bit lengthy for any problem? (Not like they are waiting for parts or anything)

Anyway I'm near the dealer today and will stop in to see if it is actually in the shop or sitting in the lot. If it's sitting in the lot there may be a lively discussion that will occur.

Soooo if you're experiencing what you consider rougher shifts than what is normal might want to check it out. (especially if still under warranty) May well be an issue that could lead to major problems down the road.
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      06-04-2015, 10:44 AM   #15
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Another reason why it's too bad they're phasing out MTs. So much less complicated and less prone to problems. But I get it, it's old fashioned technology to most people and most don't know how to shift.
BTW, BMW techs know a lot less than you think about fixing anything but routine problems. They frequently have to contact Germany to get diagnoses and repair advice. This could account for the excessive delay you're experiencing.
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      06-09-2015, 07:31 AM   #16
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Finally got the Z back. Had gone to the stealer and found the car on the hoist with the trany out and ripped apart. BMW had them install a couple modules before they would authorize a new transmission. The new modules appear to have corrected the problem.

Picked up last Saturday morning when service was closed. The bill stated this was "Goodwill on BMWs part, and that they had discussed with me that I accepted this as a final fix"

I had brought the car in 3 times in the past year regarding "transmission failure" error codes and they always said it was "functioning as designed". This last time I brought the car in it was before the warranty expired, however since they had it so long the warranty expired during the time it was there.

I wrote on the invoice that I had not agreed that this was a final fix and that it was not "Gooodwill" on BMWs part. The car had a history of the problem and it was brought in before the warranty expired.

So I'm just hoping the problem doesn't reoccur. If it does I might have a battle on my hands.

To add insult to injury when the tech called to say it was ready he stated one of the daytime driving lights was out and they could repair for $145. I said it wasn't out when I brought it in why don't they replace it. Said they couldn't, it was out of warranty. (Of course it was, they had it for so long) Anyway I told them to forget it. $15 for a bulb and literally 3 minutes of work and I had it done. (I realize a light bulb probably wouldn't be under warranty, but a good dealer would have replaced it anyway)

So I'm not too happy with International Motors in Milwaukee. They've been not the best in the past either. Next time I'm off to Zimbrick in Madison. I live about halfway between and they've been excellent in the past.

Sorry for the long rant. Had to let you know how things turned out.
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