97 N/A vacumm? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-23-2011, 01:29 PM   #1
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Default 97 N/A vacumm?

So I'm playing around with my Scan gauges that I finally made pods for. I have a question on vacuum. I'm pulling around 10.2 mm/hg (or is it in/hg) at idle. I noticed my friends SRT-4 pulls around 20. What is the normal vacumm at idle on an L36?
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Old 05-23-2011, 10:46 PM   #2
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IIRC, you should have less than 5" at full throttle and around 20" at idle. Check your lines and PCV.

Turn on The Weather Channel, as barometric pressure does have a small effect on NA engines.
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Old 05-24-2011, 11:51 AM   #3
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At WOT I'm pulling 0 vacuum
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Old 05-24-2011, 12:49 PM   #4
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At WOT I'm pulling 0 vacuum

Every car pulls 0 vacuum at WOT, unless you have boost from a super or turbo charger, in which case you will have positive pressure.
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Old 05-24-2011, 01:58 PM   #5
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Ok just making sure because colin had a number. How is my idle number?
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Old 05-24-2011, 04:00 PM   #6
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Ok just making sure because colin had a number. How is my idle number?

Can't answer without knowing the units of measure. There are inches Hg, mm Hg, PSI, and more. What units is your gage measuring in?
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Old 05-24-2011, 04:43 PM   #7
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Vacuum diagnositics:
  • Average, steady readings between 15-22 inches Hg (normal readings for a 60 V6 engine may be lower, i.e., 12-16 inches Hg) Possible Cause: Normal
  • Low but steady, between 12 and 15 inches Hg Possible Cause: Leakage around piston rings, late ignition timing, or late valve timing
  • Needle fluctuates or drops between 1 and 2 inches Hg at idle Possible Cause: Burned or leaking valve or spark plug in one of the cylinders is not firing
  • Irregular needle drop between 1 and 2 inches Hg Possible Cause: Sticking valve, intermittent spark plug misfire, or rich or lean air/fuel mixture
  • Normal at idle speed, but excessive vibrations at higher rpm Possible Cause: Weak valve springs; valves sticking in guides
  • Excessive vibrations at idle speed, but steadies at higher rpm Possible Cause: Worn valve guides
  • Excessive vibrations at all rpm Possible Cause: Leaky head gasket
  • Needle oscillates slowly, or drifts between 3 and 9 inches Hg lower than normal Possible Cause: Intake system leak
  • Normal at idle speed, but drops to near zero and rises to lower than normal Possible Cause: Restriction in exhaust system
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Old 05-24-2011, 05:40 PM   #8
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Can't answer without knowing the units of measure. There are inches Hg, mm Hg, PSI, and more. What units is your gage measuring in?
If it'* in PSI, then there'* nothing wrong. 10.2 psi = 20.7672 inHg, which is a perfectly normal reading at idle.
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Old 05-25-2011, 12:27 AM   #9
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Ah yes it is PSI okay all quite on the western front.
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