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Some buzz is normal
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Tue, 26 Oct 2004 08:09:51 Share Post by Email
In Reply to: Need help on the weirdest BPC issue you'll ever hear!, gavin, Mon, 25 Oct 2004 22:39:23
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I'm assuming you've got a later ('90s) car.

The early APC solenoid didn't buzz - it was on-off, and two wires. The newer BPC is spring-loaded, and there are three wires. The APC sends pulses to the BPC on two of the legs, and the variation in pulse width determines the valve position. This allows the BPC valve position to have a range of values between open and closed. The APC pulses the BPC at 75 hz below 2000 rpm, and I believe 90 hz (pulses per second) above 2K rpm. Why the difference? Because there can be a resonance with the airflow/intake valve opening.

It seems like you've done some modifications. If the airflow is different in your car, the BPC pulses could be creating a resonance with the airflow, and this amplifies the normal buzz. You may swap BPCs until the cows come home, and it'll still buzz. Also, make sure the mounting is right - you might have a mechanical resonance between the BPC and the mounting, and that is amplifying the sound, like a megaphone. Try a sandwich of some stiff rubber below the BPC base.

The old APC dropped you to base boost when the solenoid was disconnected. The new BPC is different. I always assumed that it was spring-loaded to go to base boost if totally disconnected.

This doesn't rule out something flakey, like the common to the BPC is missing or bad. But they normally do buzz, just not very loudly.

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