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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > N47 and N57 Turbodiesel Engine / Drivetrain / Exhaust Modifications > N57z 335XD boost issue, Update with link to log and screen shots
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      12-03-2020, 11:41 PM   #1
gogs_macaulay
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N57z 335XD boost issue, Update with link to log and screen shots

I have attached a picture from a log of Rpm, requested and actual boost. I am having an issue once changing gear, the actual boost goes all wavy(see picture).

The cars a late 2015 Lci 335D xdrive with 40k mileage, only modification being an intercooler and Xhp stage 3 on the gearbox software.

Car was getting logged for a stage 1+ tune. Definitely isnt a software issue. Car pulls well and feels strong. It's hard to notice but once you change gear, you do feel its not pulling as hard high up the rpm.

Odd because no matter what gear I start logging in the actual boost meets requested just fine, its only when the gears changed it goes all wavy.

Anyone seen anything like this before? No visible signs of a boost leak. Vacuum lines look okay. No usual noises related to a boost/Vacuum leak.

https://datazap.me/u/gogsmacaulay/lo...27-28-29-30-31
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Last edited by gogs_macaulay; 12-04-2020 at 03:25 PM.. Reason: Update
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      12-04-2020, 05:37 AM   #2
Eddamoo
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Very interesting, and great logging to explain your issue.

My initial thought was it could be a mapping issue in the TCU somehow modulating the wastegate to withdraw boost, but that should show on the 'Requested' line. Thats not to say that another sensor can influence the load.

Are you able to log the wastegate duty cycle? Theoretically the boost should only fluctuate like that if the wastegate is fluttering. Would be good to see if its being told to.

The fact it only happens after an upshift in no fixed gear suggests to me it could be a bug in the XHP map. I would try returning the TCU stock. Could also try removing all the torque limiters.
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      12-04-2020, 12:42 PM   #3
gogs_macaulay
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Thanks, so I've tired alpina tcu flash. Full vehicle software update including tcu & ecu. Xhp stage three, stock via Xhp then Xhp stage two.

As for wastegate duty cycle, do you know what its called on testO?

Thanks
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      12-05-2020, 04:49 AM   #4
Eddamoo
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OK so from another thread i got some translations:
-STAT_TrbChLP_rPs_WERT = Low-pressure turbocharging pressure plate - output duty.
This one is at "95" when closed and at "5" when open.

-STAT_LADEDRUCKSTELLER_ANSTEUERUNG_WERT = Boost pressure plate - output duty;
-STAT_TrbCh_r_WERT = Boost pressure plate - target duty ratio.
-STAT_TrbCh_rAct_WERT = Boost pressure plate - corrected actual position;
-STAT_TrbCh_rRaw_WERT = Boost pressure plate - actual position raw value;
-STAT_TrbCh_rSens_WERT = Boost pressure plate - actual position of sensor characteristic.
-STAT_CByVlv_st_WERT = High pressure compressor bypass valve - Status.
-STAT_TrbChLP_r_WERT = Low-pressure supercharging pressure plate - target duty ratio.

The one in bold mentions 'plate' and has a 0-100 value which correlates with boost so that will be your actual Wastegate Duty Cycle for your Low Pressure Turbo - this is the wavy line which is causing your boost to do the same! Im not sure why you have the Actual & Raw values for your HP turbo but not the LP as that would've been useful.

So we can see the surging and stalling is happening because your wastegate is being told to keep opening on the LP turbo, despite actual boost being lower than requested.

Unfortunately my knowledge runs out at this point - i suspect the issue is around the dual-turbo plumbing but i am unsure what could cause this. I would suggest you head over to the E90 forums as there will be many more N57 techies on there with the 2 turbo setup to help out.
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