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Vaccum question

670 Views 9 Replies 4 Participants Last post by  SilverJester
What should a vaccum gauge read at idle? I'm designing some evoscan gauges, and had originally set up the vac/boost gauge to read from -30 to +30. After watching the gauge I think my car might have a vaccum leak after watching the gauge. So I'm wondering what it should be reading?
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just remember that vacuum is not read in PSI, it's read in in/Hg (inches of mercury) and is normally somewhere between 17-22 in/Hg. What are you getting? Are you using the car's sensors or did you hook up an actual vacuum gauge?
^ Yeah that
yeah I know about the in/Hg. I'm using the car's factory sensor, and logging with evoscan. I'm only getting around 8-10 in/Hg. So I guess I have a vaccum leak. Any ideas on where I should start looking?
start by getting an actual gauge.
What altitude are you (actually the car)?
start by getting an actual gauge.
What's wrong with the factory sensor/evoscan?

What altitude are you (actually the car)?
Northern Indiana, I just googled it and I'm at about 700ft.
What's wrong with the factory sensor/evoscan?
Without a gauge you won't know whether it's your sensor or actual low vacuum. As far as diagnosis, you listen for a Tsssssssss noise around the intake manifold while the car is running and do a real thorough inspection of all vacuum connections hooked up to the manifold. Also, the gauge will tell you if it's fluctuating at all which can help with the diagnosis
Couple of more questions: Are you having any actual issues with unstable idle or the car nearly stalling (or actually stalling)? Those are prime indicators of a vacuum leak.
Couple of more questions: Are you having any actual issues with unstable idle or the car nearly stalling (or actually stalling)? Those are prime indicators of a vacuum leak.
It has been wavering a little (very minor) lately. I originally thought it was due to the fuel trims which I had scaled the maf 2 or 3 months ago for the bigger intake. I'll go outside soon and take look at this stuff soon. Thanks for the help.
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