[rpmaddict]

Hi. I run a BMW in the United States Touring Car Championship. We are defending our national title from last year, heading into round 2 this weekend. We switched from a Corvette to a BMW with an N54 this year and are struggling to get her working. I believe our team, collectively has read over 150 posts on forums regarding underboost and our problem is not like anything we have read or seen, therefore the new thread.

First: We are FBO with 100% brand new turbo related parts and have tried custom tunes from the best in the industry, and also have MHD OTS to fall back on. We have a JB4 but have not used it.

The car is a full race build so no emissions are in place. We are using NEW Pure stage 1 turbos with enlarged inlets.

Symptom: Car revs very slowly with zero boost.

Confirmed PROBLEM: Our wastegates are not keeping the flaps closed under acceleration. They are closed at idle. We have videos of actuator arm slowly opening upon first interaction with throttle, thus bleeding off boost. When we eventually hit about 4500rpm, then the arm will close the flap in an instant and boost kicks in. This is a very slow gain of RPM from 2000-4500. Slower than if it was completely N/A. We have tried a brand new DME with no fix.

We have replaced the following parts with NEW:

Pure stage 1 turbos
LPFP
HPFP
Fuel lines
Boost Solenoids (x2 Pierburg)
All vaccum lines
Knock sensors
Vanos sensors
Tial Spring (tried 3 rates)
TMAP (2.5 and 3.5 BAR tried)
Fuel Sensor
MAP
Throttle Body - NEW (tried 3 in total)
Pedal
Vacuum canisters
PCV
All FMIC, CP, in/outlets and related hoses NEW

DIOGNOSTICS: We have run all the normal tests several times. Vacuum is perfect. Boost-leak test shows a very very small leak at the cold intake side of the Pure Turbo aluminum housing where the clamp is, but this is not affecting pressurizing the system (not a boost leak problem as we have a zero value of boost during operation). We have verified (video) the Tial BOV is operating correctly. We can manually close the wastegates at 5in using mitivac and the diaphragm holds the rod and flapper closed indefinitely, so everything post boost solenoids is okay. We replaced 3 sets of boost solenoids and it did not improve. We checked the wired DME connections for the wastegate control and they are in-tact.

CODES:

2A12 (Evap and emissions not relevant)
2A13
2A18
2AFE
2F7B
However, the following codes come and go. we can usually can clear them but may reappear:
30CF Wastegate , activation
3100 Boost Pressure Control, deactivation

We did experience a 2CF9/2CFA, 2D09 but were fine after adaptation reset.

What we believe is happening and would like help to confirm:

The throttle body is not opening the valve/throttle plate. The DME will not send signal to boost solenoids because of this. Scanner proves the pedal position is working normal but the value for the throttle plate is not reacting as it should, thus the DME demands no boost.

What is the fix?

Thank you to the community in advance!

[ProblematicBMW]

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