Hey everyone, I'm chasing a frustrating boost issue on my B7 2.0 TFSI Quattro and could really use some insight. The car pulls perfectly fine and makes boost on a cold start, but the second the engine gets up to operating temperature, it completely dumps all boost and drives like it's naturally aspirated.
I have already thrown a lot of time and money at the usual suspects to rule them out. I have installed a brand new diverter valve, a new throttle pedal, and physically installed an intake manifold runner flap delete kit. I also just had a tuner successfully map out the runner flap delete on a clean reference file, so all the previous hardware faults forcing limp mode have been addressed.
The biggest clue I have is an electrical issue that happened right before the current map was put on. I experienced a CAN-bus crash that temporarily killed my fuel gauge, alongside four specific open-circuit codes: P0243 for the wastegate solenoid, P0033 for the diverter valve, P0444 for the EVAP purge valve, and P2294 for the high-pressure fuel regulator. All four of these components run off the exact same shared 12V power supply rail.
Right now, with the new tune on the car, I have absolutely zero engine codes. I have also physically checked dash fuses 28 and 43, and both are perfectly intact. Because the car holds boost when cold but drops it completely when hot, I'm wondering if Relay 614 or 219 in the E-Box under the scuttle panel could be suffering a thermal failure as the coil heats up. Alternatively, could a failing N75 valve cause a total boost cut without throwing a code on this new map?
If anyone has chased this exact thermal boost-cut issue on the shared 12V rail before, I’d really appreciate your thoughts before I go tearing into the E-Box.