I installed a DT BPV last weekend and it seemed to be working as advertised (definitely going into boost faster and smoother). The stumble around 3k rpm seemed to get a little worse but still reasonable. As the week progressed, the stumble became worse to the point today where I could not go into boost without the car jerking like it's lean. It was even slightly present at full throttle. My scan gauge seems to confirm this as the car goes into open loop when the stumble happens. I don't quite understand how a lean stumble can happen when I'm going into boost because a boost leak would turn the mixture rich. Does anyone have suggestions? I did not reset the computer like I should have and will try that this evening but it got worse as the week progressed. MAP readings look normal.

 

Just got back after resetting computer. It's slightly better, mainly at full throttle. Still major stumble right around 3300 rpm. At moderate throttle, it literally feels like your hitting the brakes at 3000 and then comes back to life around 4000. In higher gears, its more of a surging as opposed to one single dip in power.

 

Well I guess I'll bring this to closure tonight. I adjusted the stop on my stock valve to see how close I could get it to fully close. I tried adjusting the butterfly but started to destroy one of the brass screws holding it on so decided not to go forward with that. Just adjusting the stop made it close much better. I pulled the DT unit and re-installed the stock one (been-there-done-that factor was nice...3 hrs the first time, 1 hr the 2nd). Now the car is back to normal. There is only a slight stumble that comes in around 2800 rpm and is gone by 3300. The transition from closed to open loop as throttle is increased is also much less violent. The stumble definitely feels like a lean condition which would make sense as the DT unit produces more boost per percent throttle. I expect the MINI's fueling to be MAP-based so this shouldn't matter but apparently there is something else at play.

My experience with the DT BPV for one week is:
1. No yo-yo. I was very happy with this. Coming off of boost was nice and smooth.
2. Throttle and boost/vacuum are definitely more connected. The stock valve tends to have a flat spot around atmospheric pressure but the DT unit goes quickly into boost.
3. With the DT unit, my Scangauge was reading around 25 absolute pressure in the manifold (~10.5 psi) at 3000 rpm full throttle. When I reinstalled the half-heartedly adjusted stock unit, I was making 24.5 absolute or 10 psi at 3000 rpm.
4. While a heavy foot will cause lower mileage, I was pleasantly surprised on my 95% highway commute. I may have lost a half a mpg. I'm used to staying out of boost while accelerating unless I really need it.

Overall, I would definitely put it back in if I did not have the stumble. If anybody has any comments, I'm all ears.

 

I had the same issues a couple years back. Something about my Mini just did not like the DT BPV. Its a great item and works great for most. My car is a pre-face, I ended up picking up a brand new OEM one ( they revised them a couple of times ) and it worked great.

 

I've been having a very similar issue that I think is being caused the by DT BPV. I'm probably going to pull it out and change out the spring with a softer one. I'm hoping to find one that's slightly stiffer than stock and much softer than the DT one. That way I'll get the extra boost of the DT BPV because the butterfly will close 100% but I'll get a smoother transition into boost and hopefully no more weird spot around 3K on the highway.