The FS scantool logs MAP data as voltage and not KPA (pressure). For the engine tuning I need KPA numbers for MAP in the log. Is there a way to convert one into the other?
The graph looks to give the conversion as kPa=(V+.5)x20....at least as well as my eyes can estimate. Probably good enough for your data scaling, though
The graph looks to give the conversion as kPa=(V+.5)x20....at least as well as my eyes can estimate. Probably good enough for your data scaling, though
Larry
Sure, I'm just thrown off by your statement "looks to give the conversion as" and "as well as my eyes can estimate". Is this the conversion formula or an estimate based on a graph?
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08:13 AM
imacflier Member
Posts: 946 From: Levittown, NY, USA Registered: Apr 2002
Yes, it is an estimate based on a graph....but....it is a pretty good estmate and generates the points on the graph quite closely. Since you are trying to save a historical record, is deep precision really necessary for your needs? I thought you really needed comparison and trend data and that formula would serve quite nicely for that. If you need somethng better, you really need to know the error in the sensor....I have not seen that data.
Good luck to you in any case.
Larry
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09:08 AM
Blacktree Member
Posts: 20770 From: Central Florida Registered: Dec 2001
The graphs in the websites that Dodgerunner posted will work just fine. Anything more detailed than that is just "for entertainment purposes". Because the computers (and sensors) are not high-precision instruments.
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10:25 AM
Marvin McInnis Member
Posts: 11599 From: ~ Kansas City, USA Registered: Apr 2002
The graph looks to give the conversion as kPa=(V+.5)x20....at least as well as my eyes can estimate.
An exact fit to the Delphi graph would be given by:
kPa = 10 + ((V - 0.5) x 28.75)
V = 0.5 volts => 10 kPa V = 4.5 volts => 125 kPa
quote
Originally posted by Blacktree:
The graphs in the websites that Dodgerunner posted will work just fine. Anything more detailed than that is just "for entertainment purposes". Because the computers (and sensors) are not high-precision instruments.
Correct. And they are not individually calibrated by Delphi, so higher precision is probably meaningless. The Delphi data states an accuracy of +/- 2.25 kPa (i.e +/- 1.8% of full scale) over the range of 10 kPa to 125 kPa, which is reasonable for industrial-grade sensors of this type.
Further, the transfer curve posted on the Delphi web site is highly idealized since only two points are shown ... implying a straight line transfer characteristic. In my experience (admittedly several years ago) the transfer curve of such sensors is a shallow parabolic curve that only approximates a straight line; most manufacturers even include other electrical components to improve output linearity. For high-precision applications, temperature is often a significant source of pressure transducer error that can be difficult to characterize.
[This message has been edited by Marvin McInnis (edited 06-13-2012).]
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10:51 AM
PFF
System Bot
yellowstone Member
Posts: 9299 From: Düsseldorf/Germany Registered: Jun 2003
Because as you open the throttle, more air is allowed into the intake manifold.
Put the other way - THE REASON your engine runs faster is because there is more air in the intake manifold (by you opening the throttle) and the MAP sensor is reading that increased air.
[This message has been edited by phonedawgz (edited 06-13-2012).]
I am so confused. I though MAP voltage was supposed to rise as the throttle opened and approach 4.5-5v at WOT?
http://www.fastfieros.com/t...nd_how_they_work.htm The accompanying chart shows that low manifold pressure (engine idling) equals low MAP output voltage, and high pressure (engine at WOT or not running at all) equals high MAP output voltage.
[This message has been edited by plane (edited 06-13-2012).]
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06:07 PM
Marvin McInnis Member
Posts: 11599 From: ~ Kansas City, USA Registered: Apr 2002
Why is my MAP voltage dropping as my RPMs increase?
First, be sure not to confuse manifold absolute pressure (MAP) with manifold vacuum. Manifold pressure and manifold vacuum are the inverse of each other. Manifold pressure varies from a minimum of zero (perfect vacuum) to ~15 psi (ambient atmospheric pressure) maximum. Vacuum is usually expressed in inches of mercury with respect to ambient atmospheric pressure, and it varies from ~30 in-hg (perfect vacuum) to zero (ambient atmospheric pressure).
For a constant throttle setting, as RPMs increase the engine is trying to "suck" more air (per second) but the throttle isn't allowing any more to pass. The result is lowering manifold pressure (increasing vacuum) with increasing RPM ... again assuming that the throttle setting remains constant.
On the other hand, if RPM is kept constant the engine is demanding a fixed amount of air. The manifold pressure will increase (vacuum will decrease) as the throttle is opened and the manifold pressure will decrease (vacuum will increase) with it closed.
[This message has been edited by Marvin McInnis (edited 06-14-2012).]
