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supercharger vacuum leak really isn't?

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Old 05-17-2005, 10:59 AM
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Default supercharger vacuum leak really isn't?

All of you supercharged owners might be interested in the following:

While troubleshooting and trying to find the cause of a rough idle on my supercharged '92 SSE, I tested for vacuum leaks by spraying injector cleaner around the base of the supercharger, and although no idle change was observed when I sprayed it at the base gasket on the pulley side of the supercharger, where it is reportedly prone to vacuum leaks, or while I sprayed it around the rest of the base gasket, a BIG change was observed when I sprayed it around the butterfly valve shaft attached to the boost bypass valve - the engine stumbled and almost stalled so I stopped spraying there.

I first thought I had found a vacuum leak, but just for kicks I sprayed it on the same area of my '93 SSEi which has a smooth idle, and the engine stumbled on the '93 also.

Conclusion: It seems this area of the supercharger normally leaks air. Have any of you ever tried this?

So my hunt for the cause of the rough idle continues...
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Old 05-17-2005, 11:09 AM
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Bill, the vacuum fitting under the nose of the SC is only on the M90 (Series 2).

I currently have my SC torn down, and I can tell you the bypass shaft is not airtight. I think that'* normal.
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Old 05-17-2005, 11:25 AM
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[quote="willwren"]Bill, the vacuum fitting under the nose of the SC is only on the M90 (Series 2).

Bill, I wasn't referring to the vacuum fitting under the nose of the SC; I was referring to the base gasket on that side of the supercharger; I've read that this area of the gasket on the M62 is prone to vacuum leaks. At this point, I almost wish I had found a vacuum leak around the base gasket - at least that'd give me a clue to the cause of the rough idle. It'* no fun sitting in traffic in a car that has a rough idle.

My motivation for writing this post is to let others know that it seems normal for the shaft for the butterfly valve to leak air.
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Old 05-17-2005, 12:34 PM
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A mechanic once tried to convince me that there shouldn't be a leak there (he showed me by spraying WD-40). I couldn't think that there was anything abnormal (I must admit that I did try to stuff an O-ring in there).

I am having some idle issues of my own recently. Haven't been able to figured out what'* causing the issue, either.
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