I bought my 335i about 2 months ago, and installed the JB4 a month ago. Install went fine and the car felt faster but only marginally so. After turning on the boost gauge override I noticed the car was only peaking at 10lbs psi. Often hovering around 8-9lbs of psi.
Last week I added a little bit of corn to the car along with the flex fuel wires and STILL didn't feel that much faster, so I thought something had to be wrong.
I bought the JB4 used and figured maybe it needed a firmware update but I didn't have a PC. Anyways after the trouble of getting my hands on a PC and hours messing with the firmware to figure out I installed the wrong firmware and needed the ISO I FINALLY have the JB4 working the way it should be and PHEW. Holy Shit Batman!
Now I'm making 14-15lbs of boost as I should be, and spiking in the mid 16's. The car feels so fast! The boost also spools up wayyyy quicker and is wayyy more responsive. I didn't realize I had so much turbo lag! I thought it was laggy but this was my first FI car and I figured that's how things were. Gas mileage went up from 17mpg to 21 which isn't bad either.
Unfortunately... now I have a new problem...
When the car spools up and hits max boost or breaks about 11psi there is this hoorendous whine. I'm not sure where it's coming from but it sounds like a circus whistle or something. It's awful because here I come whistling down the street
Anyone have an idea what the issue is?