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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > does the 335Xi have the option to be RWD like an STI?



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      05-05-2016, 09:07 PM   #595
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Quote:
Originally Posted by blown07 View Post
Sorry to say but there is zero fuel savings to be had by disabling the AWD. You still have all the same mass to rotate. The difference is the the RWD takes all the extra load by having to drive the front stuff by way of the pavement.
This is actually a good point. The reason say a truck 4WD get better mileage when run in 2WD is that at least on mine, the front hubs disengage as well as the transfer case, so almost nothing driving the front wheels is rotating anymore. On our AWD cars, we don't have hubs or a center axle disconnect that disengage, so the axles, CV joints, front diff, front driveshaft and TC all are still turning and causing drag.
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      05-05-2016, 10:46 PM   #596
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Very easy to do this. Learn to code and check this website out. Disable everything minus the "e-diff" unless you have a mechanical LSD. http://www.onelapx1.com/blog/archives/01-2016 Then remove the center drive shaft.

I've been messing around with this for a few weeks and it will in fact behave exactly like a rear wheel drive 335i. The traction control still works when on but you can do burnouts without any fault codes, warning lights, etc. when turned off. The DTC mode will allow you to spin the tires a bit and initiate a powerslide, but will correct it before you get into too much trouble

The biggest problem is not having a real LSD and the e diff makes it very unpredictable around corners.

Going straight I can roast in 1st at will, and 2nd when the road is wet.
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      06-06-2016, 07:53 PM   #597
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Removed the front driveshaft again today. Some strange shit is going on.

The car has much more power compared to last year when I removed it. Probably a good 50hp more. Driving aggressively, when the wheels start to spin, I feel the throttle plate completely close when the wheels break loose. I have TC completely off. Should allow for indefinite wheel spin. 4x4! light comes one with abs/brake.

codes:

Also code 632D is present in most modules.


I'm able to wiggle the ass when I dump the clutch in 3rd/power oversteer in 2nd. Anything prolonged and I hit a brick wall. No power. Any ideas?

All I wanna do is fry my rears as it's time for new tires
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      02-25-2017, 08:58 AM   #598
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Thread Revival! I'm surprised after all these years, no tuner has tried any kind of solution to this in a map option or something. I would think Maybe @MHD could program this in the options when flashing a new map???
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      02-27-2017, 09:05 PM   #599
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Originally Posted by Subeamer24 View Post
Thread Revival! I'm surprised after all these years, no tuner has tried any kind of solution to this in a map option or something. I would think Maybe @MHD could program this in the options when flashing a new map???
I'd definitely be into this if it's safe for the car.
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      03-24-2017, 03:55 PM   #600
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Tried pulling fuses 26/50 out and my car was completely RWD, although dash was lit up with 4x4 errors and speedometer didn't work, drive for about 45 min hard and no problems. I want to drive RWD in the summer and so far I've read pulling the front shaft is the best solution without codes and able to turn off DTC
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      04-07-2017, 03:44 PM   #601
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Quote:
Originally Posted by BMW zone View Post
Disable servo motor ur in rwd town
How?
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      06-15-2017, 04:35 PM   #602
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https://www.amazon.com/Blue-Ox-BX882.../dp/B009APJ2UU

Wouldn't just running this little guy to the fuse allow for temporary rwd lols?
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      06-17-2017, 04:40 PM   #603
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Quote:
Originally Posted by 2007E90328xi View Post
Quote:
Originally Posted by BMW zone View Post
Disable servo motor ur in rwd town
How?
You just unplug the actuator.
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      06-24-2017, 01:57 PM   #604
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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 02:08 PM.
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      06-26-2017, 03:32 AM   #605
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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, 02:08 PM   #606
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Quote:
Originally Posted by mattgu40 View Post
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 ?
I have no experience in what you suggested but I don't know how good of an idea that is. For two reasons I wouldn't do that.

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 02:17 PM.
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      07-01-2017, 11:38 AM   #607
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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, 09:19 PM   #608
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Quote:
Originally Posted by carguy138 View Post
I have no experience in what you suggested but I don't know how good of an idea that is. For two reasons I wouldn't do that.

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."
I need to be able to switch from AWD to RWD on demand. I do drag race and my present setup causes me to have 4 wheels spins at the start line. My idea would be to set the car for RWD, do a quick burnout to preheat the tires for better traction, then put back the car in AWD just before the race.

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 11:42 PM.
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      07-08-2017, 09:23 PM   #609
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Quote:
Originally Posted by carguy138 View Post
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?
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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      07-13-2017, 04:26 PM   #610
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Quote:
Originally Posted by stephtech View Post
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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      10-02-2017, 11:28 AM   #611
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Quote:
Originally Posted by stephtech View Post
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.
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, 10:58 PM   #612
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Quote:
Originally Posted by Helicopter12 View Post
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?
No, here is the way it works;
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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      10-25-2017, 04:31 PM   #613
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Anyone found a solution? Probably MHD flash or JB4 or electrical switch?
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      10-26-2017, 10:37 AM   #614
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Originally Posted by chilingirov View Post
Anyone found a solution? Probably MHD flash or JB4 or electrical switch?
Long story short...no...a cobb map would be perfect imho lol
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      10-29-2017, 09:31 AM   #615
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Originally Posted by jcarv20s View Post
Long story short...no...a cobb map would be perfect imho lol
what do you mean - how is that possible with a cobb map?
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      04-29-2018, 06:32 PM   #616
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Guys anything...? Its been awhile. Did we all give up?
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