Summer Solstice Posted September 6, 2019 Report Share Posted September 6, 2019 I ran across this video. There are often questions from forum residents about the MAP sensor. This video goes into nice detail about how it works and how it is affected by various conditions. Pt1 and Pt.2 amounts to about 40 minutes. This is a general instructional video and is not Journey specific. Quote Link to comment Share on other sites More sharing options...
Bluesy Posted January 28, 2020 Report Share Posted January 28, 2020 I am not the SAME 'Asshat' as the one he refers to who corrected him on referring to the MAP as "Manifold AIR Pressure" and "He (Asshat #1) obviously does NOT know what he's talking about." Well, let me clear that up. I think Hat #1 is probably either an engineer OR he's smarter than the dude in this video, who actually IS very bright and DOES know his subject well. Unfortunately, like a lot of smart people, he won't let anyone be smarter than himself, which is the wring way to do life. The key is in the middle word. Absolute vs Air. I agree with VideoMan here that the MAP is actually sensing AIR pressure, it can be no other way. But there are TWO ways of referring to the pressure of a gas. The first, and more familiar to the general public is called GAUGE pressure. You've seen "PSIG" all over the place, right? Well, that 'G' at the end stands for GAUGE. As in 'Pounds Per Square Inch GAUGE'. As an engineer, I usually use the term "PSIA" when speaking of the pressure of a gas. PSIA means 'Pounds Per Square Inch ABSOLUTE'. The difference is what we refer to as 'Atmospheric Pressure". At sea level, that is 14.7 pounds per square inch. It is the weight of a column of air ONE INCH SQUARE that extends from sea level to what we call the upper limit of the atmosphere. That is an "absolute" pressure, it has no REFERENCE point except that of NO pressure AT ALL. GAUGE pressure, on the other hand refers to a gauge that has mechanisms in place that REMOVE the 14.7 psi from the reading FOR you. This is GAUGE pressure. But there are ABSOLUTE gauges out there. A good example is the gauges used in air conditions and refrigeration work. THEY are measuring the pressure inside a closed system that doe not in any way communicate with the outside, The pressure inside that system is ...wait for it....absolute. That pressure does not have to account for the weight of air, it is measuring only the pressure of the gas in the system. back to the show... The MAP sensor is actually measuring the ABSOLUTE pressure within the manifold, not the GAUGE pressure. The difference here may just be semantic to you, but to engineers, it denotes a vastly different type of fish. While the manifold does directly communicate with the outside air, the pressure inside the manifold is not created by the outside air directly, but rather by the sucking action of the pistons pulling air into the manifold. And in this sense, we are dealing with an ABSOLUTE pressure, not a GAUGE pressure. So the CORRECT term IS Manifold Absolute Pressure. Thank you. We now return you to your regularly scheduled programming. jkeaton, OhareFred and detroitgrip 1 1 1 Quote Link to comment Share on other sites More sharing options...
OhareFred Posted January 28, 2020 Report Share Posted January 28, 2020 LOL I would never argue with you! jkeaton 1 Quote Link to comment Share on other sites More sharing options...
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