Low Boost - 36 inHg MAP sensor reading + spercharger noise - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-08-2006, 11:45 PM   #11
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Ohhhhhh, I got it off an '87 Gran National :P

But really, I'm reporting what the Manifold ABSOLUTE Pressure sensor says whan I have my scanner hooked up to my car because I don't have a boost gauge. 36 inHg is indeed 17.7 psi, but to get boost you have to subtract 14.7 psi of atmospheric pressure to get 3 psi of boost. I should have 8 psi of boost: that'* 14.7 psi (atm) + 8 psi (boost) = 22.7 psi total which is 46 inHg (what I should be seeing, but I'm not).

So, somewhere along the line I'm missing 5 psi (and it'* not making me happy). Maybe (I can imagine) I got the engine that flows so well that the blower is only able to make 3 psi of boost (probable not, though).

36 inHg = 3 psi boost (now)
46 inHg = 8 psi boost (healthy blower)
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Old 05-08-2006, 11:47 PM   #12
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Another thing, when scanning my friends '97 L67 LSS with a 3.4 pulley, I saw the MAP peak at 52 inHg, which would be about 11 psi of boost, so I know the map should read around 46 with a stock set-up.

Or am I crazy? What have you guys seen the MAP read on a scanner????????
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Old 05-08-2006, 11:57 PM   #13
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Forget the MAP. Get a cheap boost gauge and get it installed. You may simply have a vac leak near the MAP sensor.

Or very carefully search for a vac leak with carb cleaner at idle. spray each connection. If the idle changes, you found your leak.
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Old 05-09-2006, 06:03 PM   #14
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I guess until I get a real boost gauge I don't really know what the boost is.

It'* just so darned convient to use a scanner and the MAP sensor in a car without a boost gauge from the factory.
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