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-   -   Low vacuum from boost controllers (https://www.jb4tech.com/forums/showthread.php?t=66463)

Tognot 09-12-2021 09:44 PM

Low vacuum from boost controllers
Recently bought a “project” . 09 535i 6spd. 130k miles . I’ll skip all the original problems and fast forward ( after many hours and parts) to where it sits now.

New OEM turbos, all intakes, hoses, oil pan gasket, w pump, radiator, walnut blast and more.

Problem: 4 psi boost. I have measured this a couple of different ways and I’m sure it’s correct. Also, I owned a n54 in the past and have an idea how it should pull.

Diagnosis done: over 25” of vacuum TO boost solenoids at idle. I tee’d into the vacuum lines FROM the solenoids to the turbos and read the vacuum when driving. At first, car pulls hard for about 1/2 second ( and vacuum to turbos/ waste gates is over 20”). Then vacuum drops to maybe 5” and so does the power. It holds about 4psi boost under sustained full throttle.

My thought: computer is killing the duty cycle on the BC solenoids and also the vacuum. I can’t find info with enough detail that describes the circuit and parameters of the BC solenoids and what affects their duty cycle.

Only code is 2AAF. I have searched for a couple days and found no similar problem but maybe ( obviously) missing something here. Thanks in advance for help “

Steve @ BMS/Fuel-It! 09-13-2021 10:13 AM

We'd need to start with a JB4 log and go from there. ;)

Tognot 09-13-2021 11:14 AM

Don’t have a jb4. Car is stock and likely will stay that way as a daily.
Out of curiosity, what would a log show that I can’t get ( admittedly not as easy) with scan tool ….for this problem.?

If the answer is duty cycle on solenoids, then that would be helpful. Not sure I can get that with a scan tool.

Thanks for a reply

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