2011 135i very unresponsive and not building boost

[SuchFinessse]

Sorry for formatting, I’m on mobile.

For a little background, its a 2011 135i DCT, upgraded charge pipe, intercooler, and catless downpipe. It’s been running MHD stage 2+ for the last 40k miles, currently at 129k. Also flashed TCU with xHP stage 3 about 30k miles ago. No issues with driveability ever. Never left me stranded.

The past month, the car has been running very weird. Just driving around town, its noticeably sluggish and will sometimes buck off the line. It’s never been this way before. If I need to get around a car in town, I used to have enough torque, in whatever gear I was in, to pass. Now, I have to drop 2 gears to get around someone. On the freeway, it’s a whole other nightmare. Merging on, I need to drop to 2nd, floor it, and be glad my transmission shifts fast, because there’s no boost. And I don’t mean no boost at all. Once you’re already on it, it feels like its making about 12psi, but that’s much lower than what stage 2 should be. The immediate surge of torque I used to get is completely gone. I used to be able to pass on the freeway in 7th. Now I need to be in 5th. It doesn’t make any low end grunt at all these days, like the turbo is disabled under 3500 rpm. Even flooring it off the line feels slow. It doesn’t seem to make even the 12psi I’m guesstimating until above 3rd gear. It almost feels NA under 3rd gear, or under 3500rpm in any other gear. And its 100% not a boost leak, this is far from the many I’ve had in the past. At least when I’ve had boost leaks before, the throttle and engine would still respond to my inputs, just with no boost. This car is making boost, it just feels like the car is guessing the throttle input, guessing how much fuel its dumping, guessing how much air it’s adding. Its like the car is confused. Ive retuned the ECU and TCU with the same tunes its been running like 4 times each and nothing has changed. I’ve scoured the forums and I’ve read many similar things, but nothing quite pinpoints my issue. I’ve read it could be the boost solenoid, wastegate actuator, HPFP, water pump, intake manifold needs blasting. A bunch of stuff. But I’m not sure what to make of it. I should mention, the car is going to the shop next week to address a couple of minor leaks; the oil pressure sensor(yes, I’m sure), the oil leveling sensor, and both sides of the charge pipe seem to have oil on them, though I’m told its blowby. I also should mention that I cannot recall the last time spark plugs were replaced, but I’m not getting any misfires at all. I’ve also thrown a bunch of codes consistently that I’ll post below:
2CF4
2D11
387F
3BD4
3BD8
3BD9
3BDB
3BDF
3BE1
CD8F

I hope all this information helps, and I appreciate any help ahead of time. This has been such a headache.

[1'M Blue]

Hi,

You might want to post it in the 135 forum section ... this here is the 1M coupe sub forum .

[SuchFinessse]

Originally Posted by 1'M Blue

Hi,

You might want to post it in the 135 forum section ... this here is the 1M coupe sub forum .

My apologies and thanks! I’ve never posted to a forum before. I’ll do just that.

[PRTSB1M]

Originally Posted by SuchFinessse

Sorry for formatting, I’m on mobile.

For a little background, its a 2011 135i DCT, upgraded charge pipe, intercooler, and catless downpipe. It’s been running MHD stage 2+ for the last 40k miles, currently at 129k. Also flashed TCU with xHP stage 3 about 30k miles ago. No issues with driveability ever. Never left me stranded.

The past month, the car has been running very weird. Just driving around town, its noticeably sluggish and will sometimes buck off the line. It’s never been this way before. If I need to get around a car in town, I used to have enough torque, in whatever gear I was in, to pass. Now, I have to drop 2 gears to get around someone. On the freeway, it’s a whole other nightmare. Merging on, I need to drop to 2nd, floor it, and be glad my transmission shifts fast, because there’s no boost. And I don’t mean no boost at all. Once you’re already on it, it feels like its making about 12psi, but that’s much lower than what stage 2 should be. The immediate surge of torque I used to get is completely gone. I used to be able to pass on the freeway in 7th. Now I need to be in 5th. It doesn’t make any low end grunt at all these days, like the turbo is disabled under 3500 rpm. Even flooring it off the line feels slow. It doesn’t seem to make even the 12psi I’m guesstimating until above 3rd gear. It almost feels NA under 3rd gear, or under 3500rpm in any other gear. And its 100% not a boost leak, this is far from the many I’ve had in the past. At least when I’ve had boost leaks before, the throttle and engine would still respond to my inputs, just with no boost. This car is making boost, it just feels like the car is guessing the throttle input, guessing how much fuel its dumping, guessing how much air it’s adding. Its like the car is confused. Ive retuned the ECU and TCU with the same tunes its been running like 4 times each and nothing has changed. I’ve scoured the forums and I’ve read many similar things, but nothing quite pinpoints my issue. I’ve read it could be the boost solenoid, wastegate actuator, HPFP, water pump, intake manifold needs blasting. A bunch of stuff. But I’m not sure what to make of it. I should mention, the car is going to the shop next week to address a couple of minor leaks; the oil pressure sensor(yes, I’m sure), the oil leveling sensor, and both sides of the charge pipe seem to have oil on them, though I’m told its blowby. I also should mention that I cannot recall the last time spark plugs were replaced, but I’m not getting any misfires at all. I’ve also thrown a bunch of codes consistently that I’ll post below:
2CF4
2D11
387F
3BD4
3BD8
3BD9
3BDB
3BDF
3BE1
CD8F

I hope all this information helps, and I appreciate any help ahead of time. This has been such a headache.

Sounds like possibly a bad transmission control module (TCM) from looking up the codes.

Link to all the codes for N55 cars
https://www.e90post.com/forums/showt...php?p=10090964

[SuchFinessse]

Originally Posted by PRTSB1M

Sounds like possibly a bad transmission control module (TCM) from looking up the codes.

Link to all the codes for N55 cars
https://www.e90post.com/forums/showt...php?p=10090964

This ended up being the case. This whole time, I ignored those codes. I thought they had to be wrong because the car drove great, but over time, it got slightly worse and progressed to where I was.

About an hour ago, I decided to try a reflash. I did a little research on xHP’s FAQ and discovered that if you have MHD flashed on your car at all, you will need to reflash MHD and change the transmission option to manual. I’m guessing that when I flash with the DCT selected, MHD will apply their own TCU tune and it interferes with xHP. As soon as I reflashed MHD and xHP (for good measure), the car drove amazing again.