2016 M4 DCT "free rev" between gears 1-2, clunk going into reverse

Narcosis

Corporal
Dec 14, 2016
149
86
0
Hudson, WI
Ride
F82
Has anyone with a 7 speed DCT experienced anything like I'm describing below?

I bought my car in 2019, it had come off lease. I've only used launch control 8 times, at the track in spring 2022. Being that it's a lease return, perhaps the previous driver launched the crap out of the car. (?) 48k miles. The tranny is tuned with xHP stage 2.

Last year I began noticing the occasional "free rev" between gears 1-2, prior to taking it to the track. The first time was slowly driving through a parking lot during the 1-2 shift in "D" mode. Light pressure on the throttle and the car rev'ed to 2500-3000 rpm between gears, got off the throttle and proceeded in 2nd. I experienced the same behavior driving through our neighborhood. Occasionally the same occurs between 2-3, always with light throttle.

Post modification, the car also has the occasional hard time idling, hunting for the idle target, and will sometimes die at a stoplight while sitting around 750 rpm. I went through some tune iterations with Wedge hoping that the idle issue could be addressed, but so far no luck. I've got a BMS BOV kit, which allows unmetered air into the loop while idling, and BMS has assured me it should not affect idle. This has caused me to think about the interface between the input shaft/TCM/clutches/DCM, and if something may be borked in the tranny / power train. There's also the occasional thunk when engaging reverse, which isn't something I enjoy.

That initial tap of the throttle to get the transmission to engage does occasionally cause the car to surge a bit, more than I'd expect.

So I'm planning to have my local indy shop (ex BMW tech has his own business, he's done a fair amount of work for me and other enthusiasts in the area) drop the transmission & determine if anything is amiss. While the tranny is out the clutches should probably be replaced with something that'll be better at holding the 675 lb/ft. Dodson is big $$, other recommendations for aftermarket clutches?

Thanks.
 

Motown65

Lurker
Sep 12, 2022
22
3
0
if you got mhd or whatever flash to the gts tcu tune and see if it goes away. If not i can try to help you with xhp settings. At 50k you may want to do a full dct refill kit from fcp. also stage 3 xhp is 20 bar so factory clutches should be fine till your built motor or more.
 

Narcosis

Corporal
Dec 14, 2016
149
86
0
Hudson, WI
Ride
F82
Thanks for the input guys. Flashing to stock is an option, just need to run the current tank of E85 close to empty.

@Motown65 I'm interested in xhp input, thanks!

Mods:
  • Agency Power intakes
  • RB2 turbos
  • MHD - Wedge E85 tune & AIC 1 map
  • xHP stage 2
  • VRSF downpipes
  • VRSF charge pipes
  • VRSF intercooler & heat exchanger
  • Vargas spline lock crank hub solution
  • Precision Raceworks stage 4 LPFP, fuel lines & FPR
  • BMS J pipe with BOV
  • EOS intake manifold
  • EOS port injection w/560cc injectors
  • AIC 1 PI controller
  • NGK 95706 plugs
 
Last edited:

Motown65

Lurker
Sep 12, 2022
22
3
0
Thanks for the input guys. Flashing to stock is an option, just need to run the current tank of E85 close to empty.

@Motown65 I'm interested in xhp input, thanks!

Mods:
  • Agency Power intakes
  • RB2 turbos
  • MHD - Wedge E85 tune & AIC 1 map
  • xHP stage 2
  • VRSF downpipes
  • VRSF charge pipes
  • VRSF intercooler & heat exchanger
  • Vargas spline lock crank hub solution
  • Precision Raceworks stage 4 LPFP, fuel lines & FPR
  • BMS J pipe with BOV
  • EOS intake manifold
  • EOS port injection w/560cc injectors
  • AIC 1 PI controller
  • NGK 95706 plugs
Post up a log of a pull
 

Motown65

Lurker
Sep 12, 2022
22
3
0
You can also adjust at what rpm the car starts grabbing the clutch when dsc is on if pull away isn’t smooth I’d probably lower it
 

Narcosis

Corporal
Dec 14, 2016
149
86
0
Hudson, WI
Ride
F82
I made the xHP adjustments and it did feel smoother, thanks for that @Motown65. Did the transmission oil & filter replacement, just to be sure. The car was driven & still shifting oddly, my indy shop pulled codes with ISTA and there were some odd ones. Cleared them with ISTA & drove it and subsequently the tranny wouldn't stay in reverse. I pulled the codes with xHP, per the attachment. The transmission is coming out & first order of business is to inspect / clean up the mechatronics module.
 

Attachments

  • transmission error codes.png
    transmission error codes.png
    1 MB · Views: 12

Motown65

Lurker
Sep 12, 2022
22
3
0
I made the xHP adjustments and it did feel smoother, thanks for that @Motown65. Did the transmission oil & filter replacement, just to be sure. The car was driven & still shifting oddly, my indy shop pulled codes with ISTA and there were some odd ones. Cleared them with ISTA & drove it and subsequently the tranny wouldn't stay in reverse. I pulled the codes with xHP, per the attachment. The transmission is coming out & first order of business is to inspect / clean up the mechatronics module.
Unfortunately this is a rare occurrence from what I’ve seen. Have you tried using ista to reset adaptations?
 

Narcosis

Corporal
Dec 14, 2016
149
86
0
Hudson, WI
Ride
F82
Yes, reset adaptations was done. The tranny is out of the car, there was a lot of metal on the shifter position sensor and input & output sensors. Hopefully the metal was the issue, reading when it wasn't supposed to or not reading when it should. Tranny should be back in the car today, all my fingers & toes crossed.
 

Attachments

  • before 1.jpg
    before 1.jpg
    89.7 KB · Views: 11
  • after 1.jpg
    after 1.jpg
    94.5 KB · Views: 12
  • before 2.jpg
    before 2.jpg
    96.3 KB · Views: 9
  • after 2.jpg
    after 2.jpg
    100.9 KB · Views: 13
Last edited:

Narcosis

Corporal
Dec 14, 2016
149
86
0
Hudson, WI
Ride
F82
Well, not the news I was hoping for. Tranny is back in the car, the test plan was run and executed as expected. It drives like it did prior to dropping the tranny, and thre During the test plan run, the rod (s?) in the unit was hard enough to feel in the drivers seat, the car almost wanted to move. Same error codes showed up, drove the car a bit more and I'm now looking for used transmission.

Anyone know of a good used DCT for sale?
 

aus335iguy

Colonel
Nov 18, 2017
2,248
803
0
Down under
Ride
335i DCT 2009
Flash the transmission back to stock ie remove xhp

you can see the number of launches in ista look for rennstart or similar

The metal is common/fairly normal as the solenoids and sensors are magnetic. It can cause issues

I’d revert to stock tune and see if your problem changes I’d say though by the sounds of things it’s clutch engagement problem
Have you tried “Kisspoint adjustment”?
Adaptations does not change this from memory
 

Narcosis

Corporal
Dec 14, 2016
149
86
0
Hudson, WI
Ride
F82
Tranny is in the car, a few miles put on to run through all the gears. Next up is executing the test plan again to allow the TCU from my original tranny learn the new unit, and hopefully the car will be back in my garage early this week.
 

Narcosis

Corporal
Dec 14, 2016
149
86
0
Hudson, WI
Ride
F82
I wanted to get some miles on the car before reporting back. Initial startup and drive was smooth, no hiccups. I reflashed xHP stage 2 and my MHD E85 map from Wedge. The light throttle blip to get into gear is now a smooth engagement vs hitting a bit. I took a road trip from near Mpls/St Paul to Des Moines last weekend to get miles on. I never knew this transmission could shift so nicely, I guess it's been in questionable shape since I bought the car, after it came off of a lease. That and I'd not driven this transmission prior to this car, and thought what I was experiencing was 'normal'.

I got on the throttle once during the road trip, for no reason. Once I was home I gave it a few good thrashings and am very happy to report that it 's shifting as smooth as butter. The cold start hunt for idle seems to be gone. That initial blip to engage 1 or R just begins to move the car vs the 'hit' I felt before.

My TCU was moved from old to new used, the test plan was executed and life is good.