Datalog N54 ST losing boost. HELP!


New Member
Aug 21, 2023
Hello, I'm fairly new to the forum and this is my first post, so I apologize if it ends up in the wrong place. I am in desperate need of help.

I have been having a problem for the last 3 months now where the boost builds to around 20psi and then it drops off quickly. By the time the half engine light comes on, it is down to 6psi and I have wastegates that normally sit between 10-12psi.

This issue happened suddenly. We were in the process of street tuning the car remotely on E85. We started from wastegate pressure, then worked our way up to 20psi. The car made POWER. We then increased the boost from 20psi to 25. When putting this tune in, I enabled MHD launch control and anti-lag in the flash options. When I went to do a pull, this issue happened for the first time. I then reverted to the previous tune and undid the changes in flash options and the problem remained. When this issue happens all of the turbo noises go away and it sounds naturally aspirated with about as much power as you would expect from a naturally aspirated inline 6 (maybe a tiny bit more) The 30FC code comes on with the half engine light if I stay on the throttle.

When I asked for help from my tuner he would not respond. For weeks. When he finally looked at the log he said my wastegates are opening. However, the pressure is still rising at its normal rate, then falling to much less than wastegate pressure. Also I have external wastegate dumps, so if the wastegates are open I would hear raw exhaust, which I do not.

Let me tell you what has been done to the car. I run a Doc Race top mount single turbo kit with a Precision 6266 ball bearing turbo. Tial external wastegates, Tial blow off valve, VRSF intercooler, BMP front facing manifold, all upgraded charge pipes, couplers, and clamps. I use a Motiv Reflex with a custom tune. I am on flex fuel and I have 750cc injectors. This car is using single bank fueling. If you have any questions on the car, let me know. T

I have done a whole lot to attempt to diagnose this car.

The most major change I did was installing the aftermarket after I found a small crack in the plastic intake manifold.
I tested for boost leaks since then with a high pressure smoke tester. I found nothing.
I tested the wastegate line setup separately from the rest of the intake system and there are no leaks there. I have not made any routing changes since before the issue started happening.
I tried changing map sensors
I tried removing the BOV spring and put something solid in there to it stuck shut
I tried swapping bank 1 and bank 2 wastegates
I tried resetting the reflex, flashing back to stock, and reinstalling software

I have tried so many different things, as I think of them I will list them better.


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