Author Topic: Barometric pressure of 24.8??  (Read 6946 times)

Offline beveryafraid

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Barometric pressure of 24.8??
« on: May 13, 2011, 06:03:29 PM »
I just got my gauge this afternoon and took it for a spin, but have not calibrated anything yet. I did cycle through some non-default gauges to see how easy it is to change displayed items. I saw that my barometric pressure showed 24.8 whether the car was running or not. Since it's in inches of mercury like a weather barometer or an altimeter in an aircraft, it seems strange that my local pressure would be 24.8, since most barometers show in between 28 to 32 inches of mercury. An average local baro reading is usually in between 29.80 and 30.40 in most weather, fair or bad. So I may have something wrong with a sensor in my car possibly? When I flew aircraft when younger most altimeter setting were in the same range I just mentioned. I'm at 4700 feet elevation and I think that it's possible that this is absolute air pressure not adjusted to sea level like a weather barometer is. Meaning it's possible that is I were at sea level near a coast that it would read a more normal reading like I'm used to. But I'm not enough of a geek to figure this out. Anybody else have a clue?

Offline UltraGauge Admin

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Re: Barometric pressure of 24.8??
« Reply #1 on: May 13, 2011, 06:32:56 PM »
I just got my gauge this afternoon and took it for a spin, but have not calibrated anything yet. I did cycle through some non-default gauges to see how easy it is to change displayed items. I saw that my barometric pressure showed 24.8 whether the car was running or not. Since it's in inches of mercury like a weather barometer or an altimeter in an aircraft, it seems strange that my local pressure would be 24.8, since most barometers show in between 28 to 32 inches of mercury. An average local baro reading is usually in between 29.80 and 30.40 in most weather, fair or bad. So I may have something wrong with a sensor in my car possibly? When I flew aircraft when younger most altimeter setting were in the same range I just mentioned. I'm at 4700 feet elevation and I think that it's possible that this is absolute air pressure not adjusted to sea level like a weather barometer is. Meaning it's possible that is I were at sea level near a coast that it would read a more normal reading like I'm used to. But I'm not enough of a geek to figure this out. Anybody else have a clue?
That particular parameter is read directly from the ECM and displayed unaltered.  24.8 is low, in fact lower than the lowest ever recorded.  It would seem something is out of whack with your vehicle's barometer.

Offline bamzippow

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Re: Barometric pressure of 24.8??
« Reply #2 on: May 14, 2011, 09:03:43 AM »
What year/make/model do you have?  ;)

Offline beveryafraid

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Re: Barometric pressure of 24.8??
« Reply #3 on: May 15, 2011, 12:33:14 AM »
No worries, I have figured out that these sensors on vehicles are reading "absolute" barometric pressure. It's the raw barometric pressure that has not been corrected for sea level pressure. A typical barometer, which is usually the aneroid type that you might have on your wall is supposed to show sea level pressure even if your location is well above sea level. I think I was right when I mentioned that this sensor would read a more normal barometric pressure is I was down at a coastal location. But I'm at 4760 feet above sea level in Utah. I bet if other people that read this thread are at a high elevation and read their Ultra-Gauge barometric pressure inHG then they would get a pretty low reading like mine, since it's absolute barometric pressure. I have since done away with this gauge to read something more useful, I was only curious about it.

Offline beveryafraid

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Re: Barometric pressure of 24.8??
« Reply #4 on: May 15, 2011, 01:04:26 AM »
By more research, I have confirmed what I said. In the link below there is a table and if you go to 5000 feet, it shows average absolute pressure at that altitude to be 24.9 inches of mercury. And at sea level it's 29.9, which I already knew. And with variations of weather, it can rise and fall higher or lower like pressure always does. So my reading of 29.7 would correspond to a sea level reading of 29.70 inHG. Here's the link for you fellow geeks who care: lhttp://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

Offline tfuk

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Re: Barometric pressure of 24.8??
« Reply #5 on: July 14, 2011, 11:47:56 AM »
You are right, the 24.9 inches Hg is normal air pressure at 5000 ft elevation above sea level.
The value corrected to sea level is important for weather but the absolute value is important for you car for accurate fuel injection.