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Re: buzzing under hood Posted by Ari [Email] ![]() ![]() In Reply to: buzzing under hood, Nick Urban, Sun, 31 Oct 2004 16:17:44 Members do not see ads below this line. - Help Keep This Site Online - Signup |
As the other folks have said, this is the Boost Performance Control (BPC) valve. It decides how much air pressure gets to the turbo wastegate actuator. It's job, along with the wastegate actuator, is to control turbo boost.
It is normal for the valve to buzz. It gets pulses at 75-90 hz (pulses per second) to control boost. It gets these pulses all the time; the duty cycle (on-off ratio) of the pulses from two of the leads sets the valve position. So even at idle, it's controlling.
Some buzz louder than others. With the key ON and the engine not running, the engine is pretty quiet, so hearing the buzz isn't unusual. All it takes is a little resonance with the radiator shell, and it can get pretty loud. Even with the engine running, there can be resonances that can make it loud - Saab even programmed in frequency change (75-90 hz) to avoid resonances with intake air, which can get loud.
So a loud BPC isn't necessarily a sign of a bad one. If you're getting full boost, and things are nice and normal, no problem. Especially if you can't hear it with the engine running.
I'd put this down as a Don't Worry.
posted by 192.249....
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