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 Post subject: Low Boost
PostPosted: Fri Sep 14, 2012 1:22 am 
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Year and Trim: 1994 Pontiac Bonneville SSEI
Ok, couple questions.
1. Due to lack of oil the supercharger ran dry which wore its bearings which wore the inside of the body, so could this wear cause almost a complete loss of boost?
(needle may move slightly)(Also bearing have been replaced)
2. Before the damage the boost gauge read -70 idling. Now the Boost gauge reads -5 to 0 why is that?
3. If the wear couldn't cause the loss of vacuum/Boost what could? (I've checked the BCA and am pretty sure it's working correctly Still need to check the BCS but doubt it's that)

Any help would be appreciated, I always assumed that the wear was causing the loss of Boost but the loss of vacuum confused me. Unfortunately I can't trouble shoot for the next day or two as i have the steering column disassembled and little time to work on it. When i get a moment I'll do a more thorough check on the Vacuum tubes and do some off the problem solving test such as removing Vac line from BCS + BCA seeing if boost rises and arm properly Extends/Retracts.

P.S. I vaguely remember rebuilding the supercharger think it was a .1mm-.2mm gap between the rotors and the body. Although I really couldn't say for sure it was about 2 years ago.

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 Post subject: Re: Low Boost
PostPosted: Fri Sep 14, 2012 11:11 am 
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It sounds as if you may have a break in the vacuum line leading to the BCS. A common failure is the vacuum T in the LIM under the supercharger snout.

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 Post subject: Re: Low Boost
PostPosted: Fri Sep 14, 2012 12:22 pm 
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A 94 won't have the t-fitting under there. The boost reading comes from a line that runs from under the MAP over to the vacuum tree near the front driver side corner of the SC case.

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 Post subject: Re: Low Boost
PostPosted: Fri Sep 14, 2012 12:28 pm 
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So, it was all damaged and you rebuilt it yourself? What all did you rebuild? I'm just wondering if the seals for the bearings in the center rotor plate aren't leaking because they were damaged...

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 Post subject: Re: Low Boost
PostPosted: Fri Sep 14, 2012 11:36 pm 
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Year and Trim: 1994 Pontiac Bonneville SSEI
Thx for the replies.

Would a leak in the vacuum line cause any other effect to the engine that might help me identify it quicker?

@00Beast Like i said the repairs where done a few years ago and I'm struggling to remember what was repaired. I think the rotor bearings where done and i think most seals, or any that where removed where done. It was just to ensure no more wear could occur. Would this kind of leak make a noise? (not that it's easy to hear a slight noise with a engine revving right below it.)

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 Post subject: Re: Low Boost
PostPosted: Sat Sep 15, 2012 11:37 am 
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J Wikoff wrote:
A 94 won't have the t-fitting under there.
Oops. I should have paid more attention to the year.

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 Post subject: Re: Low Boost
PostPosted: Thu Oct 25, 2012 9:15 pm 
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Year and Trim: 1994 Pontiac Bonneville SSEI
Just so everyone knows it was a couple disconnected vacuum pipes very little loss in actual boost and engine runs a lot better now i just gotta get on top of the front struts and the blower control module so i doesn't look like I'm driving a lowrider when i hit bumps.

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