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Old 09-12-2006, 12:57 PM   #71
Scooby Specialist
Member#: 56468
Join Date: Mar 2004
Chapter/Region: NWIC
Location: Seattle, WA
04 Improved STI
Dirty White


I guess it's possible, but it does not sound like surge to me. Surge is more of a honking noise.

This begins to occur at light to medium throttle, ~4000 RPM and slight vacuum (10-50 mm Hg). I know it's related to AVCS because when I turn off the solenoids the sound disappears. Also if I lower the advance in the AVCS map the sound disappears.

I have many fears about why I'm getting the noise, but right now I'm just trying to figure out what the hell is making it.

If you have ever listen to a motor thru det cans that's what it sounds like. It's as if someone opened a little window on the valve cover and all the sudden you could hear the valves better. It's not loud. It a pffft,pfft,pfft,pfft or a thfft, thfft, thfft, thfft that increases exactly with RPM and it's dependent on active AVCS.

To get rid of the noise I need to retard the AVCS substantially, like 1/3 less advance. It began making this noise after a rebuild with higher compression pistons. I tuned out the noise, but I am still wondering what the hell it is + I'm looking for a cause (e.g. is it a indication of lowered oil pressure? I'm getting gauge).
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