So, ever since the Mini got back on the road, I’ve felt like it’s been...off. Something hasn’t been quite right. It just felt down on power, some times moreso than others. I wasn’t throwing any engine codes, so I didn’t really know where to look. After hooking up my OBDII adapter and firing up both DashCommand and Torque Pro, I noticed my boost levels were low. Like, really low. Vacuum levels seemed a tad off too.

And thus began the 2 week long hunt for a vacuum leak. I traced lines. I seafoamed the car in hopes that maybe it was just carbon buildup. I fiddled with bits and pieces and just generally spent a lot of time ripping my hair out while Googling possible outcomes.

I finally bit the bullet and made an appointment with a well-recommended local shop to have the car checked out and given a smoke test to check for vacuum leaks.

Turns out the vacuum system is tight as a drum. Not even a hint of a leak. Nor is there any hint of a boost leak. But the system was still not producing boost. On a whim, we decided to take a peek to see if the bypass valve was opening and closing on command. I tried this a couple of days ago and didn’t see anything obviously amiss, but I felt like the tech may have better luck.

Yep.

The bypass valve itself is fine. But what you see circled is where the hinged stop plate is supposed to pivot down as the valve opens and closes. Somehow the throttle body bracket got tweaked just enough to impede the movement of said plate, causing the bypass valve to only partially close, meaning I was constantly letting air leak past the supercharger, straight to the intake.

The leak itself wasn’t severe enough to trip a fault code, but it essentially removed almost all of the boost I was supposed to be making. Once I got home, I took the bracket off and filed down that corner of it before putting it back on and making sure it was positioned out of the way of the plate. Just an extra millimeter of clearance makes all the difference with something like this.

After driving the car, I can say it’s a night and day difference. I hadn’t realized just how down on power I’d actually been since getting the car back on the road. It’s like I have double the torque I used to and throttle response is worlds better. It was just one of those really small, really obscure little things that 20 mechanics can look at and not see.