BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > What exactly fails in the boost solenoids when they go bad?

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      07-17-2018, 10:43 PM   #1
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Drives: 2007 E90 335i 6mt
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What exactly fails in the boost solenoids when they go bad?

I recently replaced my boost solenoids, and on a whim took one of my old ones apart like the guy in this video.

I'm having a hard time figuring out what exactly goes bad in them. It looks like it's just a coil with a rod in the middle attached to a diaphragm. The cap that goes over the diaphragm has to nipples, one for the vacuum source and one for the wastegate actuator. There is a vent on the other side of the diaphragm that exits from the big boxy knob sticking out the top of the solenoid. So what goes bad? Does heat damage the electrical connection? Warp the diaphragm? Does crud get in the connectors? I just don't see what there really is to fail because it's such a simple device. You all are smarter than me. A little help?

Btw, our solenoids look identical to the Volvo solenoid the guy in the video was taking apart.
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      07-18-2018, 05:21 PM   #2
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Drives: Was '07-335e92 - Now '13-335IS
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selenoids generally just fail to react when they age. The process of changing them usually gets all other hardware that can also cause issues.

Apr'17 - '13 335IS replaced the '07 E92
IS mods-MFactory LSD/MHD-BQ Tuned/ATM-IC/AFE Momentum GT/Konis/Mfront&HeimJoint Rear rods&arms
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      07-19-2018, 12:44 PM   #3

Drives: 2008 135i Manual, CBR650F
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They leak off vacuum when they fail.
I got curious and opened my old one too. The electrical bit functions just fine, I believe the diaphragm deteriorates in a way that it no longer seals. I tried cleaning and conditioning the diaphragm without luck. The solenoid functions by either applying vacuum to the wastegate actuator, or leaking off that vacuum. When mine failed, it leaked off vacuum continously, so the wastegate wouldn't close and I got no boost.
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