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BMW 3-Series (E90 E92) Forum
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does the 335Xi have the option to be RWD like an STI?
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06-17-2017, 03:40 PM | #595 |
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06-24-2017, 12:57 PM | #596 |
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Haven't logged on in a while and had a few PMs about going to RWD on an XI. I answered them but will post here for everyone's info.
Basically I had fun with it for a bit but got annoyed with how easy it was to spin the tires and have the DSC come on. It behaved just like a RWD 335i and I could burn tires as long as I wanted without any warning lights or throttle cuts; on a 2011 msport 335xi with manual. A mechanical LSD would fix the issue but I haven't really found a clear answer how to do this. I'm a big fan of bolting BMW OEM parts on rather than aftermarket (i.e. if there was a simple way to put an OEM m-diff in, I would do that). DTC and DSC worked exactly the same. The one thing I notice with the Dynamic Performance Control (FDB) turned off is that the car handles a bit differently in the snow, and not in a good way. Even with the E-diff left coded on and driveshaft installed, its very apparent that the car has open diffs- compared to when the Dynamic Performance Control (FDB) is on. I suspect the reason for this is that the Dynamic Performance Control (FDB) and E-diff work together. I have zero evidence to back it up but this is what I assume is happening. Lets say you are driving in the snow with the DSC off and gas it coming out of a corner. With the Dynamic Performance Control (FDB) active, it is very easy and predictable to control the slide. With the Dynamic Performance Control (FDB) off, you can feel the inside tires start to spin and then the rear will step out (awkward delayed feeling). When wheelspin is detected I believe the Dynamic Performance Control (FDB) module cuts power and controls forward/aft torque distribution. The e-diff individually pulses the brakes to simulate a LSD. I believe that the brakes are fairly ineffective at stopping the spinning wheel under power WITHOUT cutting the throttle via Dynamic Performance Control (FDB). On dry pavement with the DSC off (10 second push) it is very hard to do donuts on asphalt. The inner front and rear tires spin. E-diff is coded ON. Anyways here is how to do it. I believe step 2 is what causes the 4x4 warning light and abrupt throttle cut during wheelspin with driveshaft removed. Unfortunately I think 2 impacts how well the e-diff works. 1) Pull front Driveshaft off 2) Dynamic Performance Control (FDB) TURN OFF from http://www.onelapx1.com/blog Dynamic Performance Control (FDB) N55 X1 Parameter: e84_FDB N54 335i xDrive Parameter: FDB To disable, set to "nicht_aktiv". This feature encompasses two things - corner braking designed to "torque vector" and redirecting the power through the xDrive system for a 20/80 FWD/RWD torque split. I am conflicted on this option, and need to do more testing on the implications. Without a doubt, this feature accelerates brake pad wear - if you are driving with a decent amount of slip angle, it will be almost constantly corner braking. Traditional logic holds that corner braking is a worse way to torque vector than mechanical LSDs are and that's probably still true, but recently supercars such as the McLaren 650S started coming with corner braking torque vectoring. Granted, the software in a McLaren is hopefully more advanced than that in an entry level sedan (BMW 335i) but the point holds - there must be something to it if supercar manufacturers are going in that direction. What is frustrating about the X1/335i is that you can't separate the 80% RWD bias (an unquestionably good thing) from the brake-based torque vectoring (possibly a bad thing)? So, what's the upshot? I think it probably goes something like this: 1. Base car without this option - code it on for a nice performance boost! 2. M-sport pack that comes with it enabled, but no mechanical LSD - leave it on 3. Car with an upgraded mechanical rear LSD - ????? 3) OPTIONAL: If you have a mechanical LSD, turn off E-Diff Electronic Differential (AX_Ref_Diff_Lock) N55 X1 Parameter: e84_AX_Ref_Diff_Lock N54 335i xDrive Parameter: AX_Ref To disable, set to "nicht_aktiv". Last edited by carguy138; 06-24-2017 at 01:08 PM.. |
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06-26-2017, 02:32 AM | #597 |
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Would there be a way to unplug the actuator and simulate the motor with some sort of resistor connected to it? Goal is to achive RWD and be able to turn the DSC off as when you just disconnect you get errors and cant turn it off.
best case senario having variable resistor (if it works this way.. im no electro-magic guru) then connect to the actuator to be able to manually set rwd fwd ratio ? any of this possible ? |
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06-26-2017, 01:08 PM | #598 | |
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1) These cars have a lot of interwoven control modules and electrical systems. 2) Brake system may be involved. Another thing that I was thinking about (and if anyone knows more, please correct me) but the portion that powers the rear wheels on a xdrive is much different than the rear wheel drive. I now believe a second clutch pack connects the transmission to the rear driveshaft as well as a clutch pack to the front drive shaft. When the front drive shaft is removed, the clutch pack to the rear is locked since the ECU believes the front wheels have zero grip. I do not know the answer to this but that may cause issues down the line. Evidence of a clutch pack for the rear driveshaft is shown in the video on here. With the ability to send up to 100% of power to the front tires, there would have to be a way to disable the rear. http://www.awdwiki.com/en/xdrive/ Long story short, this car is complicated enough and if there was a simple way to modify the drive train easily, it would have likely been done by now. Problem is with experimenting is that now you have the potential to break very expensive parts that aren't easily accessible. Now that there is a chance that the transmission isn't directly bolted to the rear driveshaft on a 6mt, I'd tread very lightly on this matter. EDITED: I might be wrong per a wiki article that I just read. Check out the last sentence, it states that the rear drive shaft is hard coupled to the transmission output. https://en.wikipedia.org/wiki/BMW_xDrive "Instead of a permanent torque split (which is featured in earlier systems), xDrive provides variable torque split between the front and rear axles through the use of a multi-plate wet clutch located in the gearbox on the output to the front drive shaft. This setup allows xDrive to modulate the torque split between the front and the rear axles, which is normally split at 40:60 ratio, respectively. If wheel slip is detected by the ABS/DSC system, xDrive can react within a tenth of a second to redistribute up to 100% of the engine power to the front or rear axle.[1] The wet clutch is applied through a high speed electric servo motor turning a cam-shaped actuator disc. As the rear drive shaft is hard-coupled to the transmission output, full torque transfer to the front axle can only be achieved if the rear wheels have no traction and are both slipping." Last edited by carguy138; 06-26-2017 at 01:17 PM.. |
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07-01-2017, 10:38 AM | #599 |
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Just had an idea for anyone very experienced with coding.
Apparently the xdrive cuts off power above a certain speed threshold. I wonder if there is a way to change this speed value or even set it at 0mph via coding. Thoughts? |
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07-08-2017, 08:19 PM | #600 | |
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I must have a way to do that without pulling the driveshaft obviously. Have you found other options in the DSC module that might be related? Do you think that If I find a way to code the option live at the track my rear tires would both spin for a burnout? I can do coding and I could also automate it.
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Last edited by stephtech; 07-08-2017 at 10:42 PM.. |
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07-08-2017, 08:23 PM | #601 |
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If someone can find the CANBUS packet sent from the DSC module to the VTG (transfer case module), then I will make that happen. I could also install a "man-in-the-middle" that could intercept the message and modify it for whatever we need.
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2010 E90 335XI 6AT with XHP stage 3 | JB4 G5 W/Trebila Tune | RB Next Gen 15T | RB hot side INLETs | ETS FMIC | VRSF CP | FORGE DV | Custom METH KIT CM10+CM5 plus MMP gen2 PI | AR design cer. DPs | BMS OCC | RB external PCV w/plugged HEAD. Best 1/4: 11.47@123mph
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07-13-2017, 03:26 PM | #602 |
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10-02-2017, 10:28 AM | #603 |
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Since it uses a stepper/servo motor to engage the clutches for the front drive couldn't one just disconnect the motor and replace it with an equivalent resistance so that the controller still thinks it is hooked up?
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10-13-2017, 09:58 PM | #604 | |
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it is not a stepper motor, it is a dc motor with hall sensors. These sensors are used to monitor the actual rotation of the motor. Then the control module monitor the motor current to determine when the clutch is actually getting applied. It would be much harder to try to fool the feddback than hacking the communication messages via canbus. In the old bmw DIS diagnostic software, there are diagnostics tests that actually talk to the control module and actually make the motor move to apply the clutch. I am pretty sure that this would be a good start to understand a bit better the communication.
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2010 E90 335XI 6AT with XHP stage 3 | JB4 G5 W/Trebila Tune | RB Next Gen 15T | RB hot side INLETs | ETS FMIC | VRSF CP | FORGE DV | Custom METH KIT CM10+CM5 plus MMP gen2 PI | AR design cer. DPs | BMS OCC | RB external PCV w/plugged HEAD. Best 1/4: 11.47@123mph
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10-26-2017, 09:37 AM | #606 |
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11-04-2018, 12:14 PM | #609 |
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Thought I'd revive this ridiculous thread with some news that we never thought we'd hear! A company called xDelete (I believe the same guys behind xHP) announced an android app (like xHP, MHD, etc.) that has the ability to switch XI cars between AWD and RWD. Apparently after 10 years someone's finally found the data table controlling the multi plate clutch inside the transfer case and can just set it to disengage completely. Slated to release in December! Lots of info here including a FAQ pdf:
https://www.facebook.com/XDelete-700128953698940/
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12-13-2018, 08:10 AM | #610 |
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xHP xDrive Disable
I saw BMW Fanatic's post on this and was curious what sort of (if any) damage you can do to your car by sending all of the power to the rear wheels.
I have AWD and would love to run RWD in every season but winter. Are rear driveline components generally the same in AWD E9X models as they are RWD E9X models? Same strength? If someone doesn't know off hand I can just reference part numbers and compare. |
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12-13-2018, 09:52 AM | #611 |
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I had the same concern, but yeah, the rear is the exact same parts. They claim it'll help save your transfer case but I've read the front diff is even more of a weak point
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12-13-2018, 10:28 AM | #612 | |
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I think this, the xDelete, is a great option for us that enjoy having AWD in the north winters and RWD for fun in the summer! Only time will tell if there are adverse effects.
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12-14-2018, 08:34 AM | #613 |
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once i swap my engine in i will try this and give feedback. The front is electronically controlled so it really shouldn’t be any concern. I imagine You install a lsd in the back and code out the e-diff and you will have a awesome car
Last edited by lhuynh336; 12-16-2018 at 07:43 AM.. |
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12-18-2018, 12:49 PM | #615 |
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12-18-2018, 12:53 PM | #616 |
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My front driveshaft u joint blew up this morning, guess I'm RWD now!!
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