N54 Powered race car needing HELP - Wastegate

[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!

[iminhell1]

The vacuum pump on the front of the HPFP is where the vacuum for the boost solenoids is sourced from. If you are loosing vacuum and there are no leaks, then Id' say it's wore and can't keep up to the demand.

BUT, make sure you don't have a leak near the vac pump. That plastic tube can crack, someone may have left the vacuum hose going to the rear muffler uncapped (vacuum leak).

Once the EGT's and RPM comes up the gates are probably full open. Depends on the tune. But generally any time you're in Spool Mode they should be closed.


Also make sure the Boost Solenoids are plumbed correctly.

[wheela]

+1 on checking that your vacuum pump is making enough vacuum, and that the exhaust flap vac line isn't open. However, I'm not sure why the wastegates are closed when idling, I'd have just assumed they'd be open since you obviously don't need boost?

I can't explain the throttle plate not responding, but if that's happening after the boost deactivation and wastegate codes are thrown it could be some kind of protective response if the dme thinks something is wrong?

[wheela]

A possible explanation for the throttle plate observations - since the dme is load based, the throttle will only open as far as necessary to hit the load target. Depending on the conditions, it won't match pedal inputs 1:1. For example, just yesterday (on a different forum) I saw a log of a guy's WOT pull with pure 600's but not tuned for it. His pedal position was 100% for the whole pull, but throttle position was about 30% for the whole pull. Nothing wrong with his throttle plate, it was just overboosting and 30% was all it needed to hit load target (it was still slighlty over load at 30%). On my old oem stock bmw tune (stock tune, and stock turbo), the first 1/3 of a WOT pull sometimes the throttle plate wouldn't be fully open yet - because load was already on target and more throttle plate wasn't needed. Maybe your seeing an artifact of this behavior?

[rpmaddict]

Originally Posted by wheela

A possible explanation for the throttle plate observations - since the dme is load based, the throttle will only open as far as necessary to hit the load target. Depending on the conditions, it won't match pedal inputs 1:1. For example, just yesterday (on a different forum) I saw a log of a guy's WOT pull with pure 600's but not tuned for it. His pedal position was 100% for the whole pull, but throttle position was about 30% for the whole pull. Nothing wrong with his throttle plate, it was just overboosting and 30% was all it needed to hit load target (it was still slighlty over load at 30%). On my old oem stock bmw tune (stock tune, and stock turbo), the first 1/3 of a WOT pull sometimes the throttle plate wouldn't be fully open yet - because load was already on target and more throttle plate wasn't needed. Maybe your seeing an artifact of this behavior?

Quite possibly it related. But the curious part is that we are now seeing boost kick in only at 5000 or higher RPM and only in gears 4 and 5. 1-3 are completely boost-free.

I am troubled with the thought that our DME can be seeing an overboost situation but not throwing the code while putting us in limp mode.

We did some more vacuum testing and we are good pre-solenoids. Even if we repeatedly hit the the brake pedal, the vacuum only drops to 20in. Thats bypassing the canisters. With canisters in the scheme, we are over 23in.
That should be enough to maintain the wastegate closure without bleed off. I don't understand if the DME is seeing this volume of vacuum, why it is necessary to divert from the solenoids. My logic is that happens only when low vacuum is seen and the solenoid for boost is sacrificed for the brake booster.

I will look into the boost target scenario. Just don't know why the codes won't show this.

Thank you for your assistance. We are turbo dumb and numb

[iminhell1]

Well if gears are involved that sounds more like the boost by gear option got checked by mistake. That's something you can do in the MHD app and isn't custom tune related.

[rpmaddict]

Originally Posted by iminhell1

Well if gears are involved that sounds more like the boost by gear option got checked by mistake. That's something you can do in the MHD app and isn't custom tune related.

First, thank you for your responses.

I really wish this were the case and we could click it to fix it. Unfortunately it is not optioned in our tune. The boost was fine for the first day of track use. The car was running so well that we blew the coupler for the VRSF boost outlet pipe.

After replacing that, it's been all down hill. We have gone with two custom tunes and even flashed back to stock with no fix. We have replaced or removed and inspected every hard part we can think, performed boot leak and vacuum leak tests to the point of nausea.

Is there any other setting or solution to this mysterious throttle closure in these gears?