Datalog N54 - Wastegate and Boost oscillation under WOT not reaching target.

elchicodeleste

New Member
Dec 12, 2022
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Hi guys, the boost of my car is bouncing from 12 to 15 psi under WOT whereas target is 18.2psi. It never reaches this point. The logs show that wastegates % oscillate too, both of them at the same very moment. I will add info about my car and also the logs (datazap link + image).
My assumptions is either solenoid in bad state/failing or turbos in bad condition but it is just an assumption and I dont want to throw money on something unnecessary. I have so much rattle, but a lot. I hope you can guide me. Thank you in advance.

My car:

135i n54 6MT with MHD Stage 2+ on 93
Dual Cone Intake
FMIC
Catless Downpipe
Chargepipe + BOV
Silicone Inlets 2"
LPFP Walbro 450

Also replaced almost everything can be maintained, brand new with less than 1000 kilometers like:

Every single gasket on the engine.
RB pcv
O2 sensors
LPFP sensor
Sparks
Coils
Turbo seals
Waterpump and thermostat
Alternator
Battery


All said, here I attach the link of the log.

https://datazap.me/u/elchicodeleste/oscillation-wgdc-hence-boost?log=1&data=4-5-23


Here you can see BOOST target and BOOST psi

eGgtHXM.png




Here you can see WGDC % and BOOST psi

glPBjGW.png
 

carabuser

Lieutenant
Oct 2, 2019
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My first thought is boost solenoids. You can verify this by running both banks off one solenoid but if they are original just replace them, I'd consider them a maintenance item along with replacing all the vacuum lines.

Boost leak is also a possibility. That's quite a strange pattern but can happen with certain leaks.
 

elchicodeleste

New Member
Dec 12, 2022
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3
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My first thought is boost solenoids. You can verify this by running both banks off one solenoid but if they are original just replace them, I'd consider them a maintenance item along with replacing all the vacuum lines.

Boost leak is also a possibility. That's quite a strange pattern but can happen with certain leaks.
Thanks for the response. Vacuum lines were replaced by silicone lines. I will replace solenoids too. Is there a way of testing they indeed fail?
 

carabuser

Lieutenant
Oct 2, 2019
870
1
766
0
UK
Ride
Z4 35i & 335i
Thanks for the response. Vacuum lines were replaced by silicone lines. I will replace solenoids too. Is there a way of testing they indeed fail?
You can run both wastegates off a single solenoid so do a log with both connected to solenoid 1 and then another log with both on number 2.

The wastegate command is the same to both turbos anyway so I think BMW just put 2 in place to provide some redundancy and maybe some slight improvement in reaction time.
 

elchicodeleste

New Member
Dec 12, 2022
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You can run both wastegates off a single solenoid so do a log with both connected to solenoid 1 and then another log with both on number 2.

The wastegate command is the same to both turbos anyway so I think BMW just put 2 in place to provide some redundancy and maybe some slight improvement in reaction time.

So I will buy the solenoids. It would be rare that both are failing but, anyway, I will try. I have tried with different maps, and same result. Also I put back on the car all OEM parts to discard that the problem was aftermarket parts, but same issue happening.
I will let you now when new solenoids are on.
Also I will buy new turbos, which I was decided to do, but now with more reason.
 
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elchicodeleste

New Member
Dec 12, 2022
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UPDATE: thanks to @carabuser I could test boost solenoids independently and found out it was one of the issue of bouncing.
With the healthy solenoid the car was able to build up 19.2 psi smoothly, without wastegate bouncing / oscillations.

I already order a brand new set of Pierburg solenoids. Don't ever buy a Chinese/eBay/amazon set of solenoids, who buys cheap buys twice. Lesson learnt.