I just finnished looking at some logging from the HPT scanner, and am a little confused by the MAP sensor. It reads from 0psi to 15psi, when my boost guage in the car reads 20 vacume to 8psi. Should they not read the same as they are both readin the air pressure in the manifold, or am I missing something?
I have the MAP sensor that came with the S/C.
I'm still confused, just talking in psi for a minute, when my boost guage is at 20 vacume (idle) the map sensor is reading 0psi, and imediatly goes up from there... When I am well into boost (~6psi) the MAP sensor is reading almost 15psi.
I just switched the VCM scanner software over to kPa, and the MAP sensor is showing a sweep from 0 (idle) to 105 (in boost).
Is this correct, to me, it seems like the scale is off?
I checked the conversions calculater in the program, and the kPa and psi seem to track the same values for the MAP sensor.
allright.
you just lost me... I've got some reading to do tommorow, and the last beer I had mad me atmospheric pressure stupid.
I'm having a similar situation with my eco s/c. The scanner was giving me readings off the charts (default charts) for kpa, so i switched it over to psi, and got values around 25+. At first I thought since I have the 2.5 bar sensor maybe I could just divide 25 by 2.5 and get 10 which sounded right...but I guess what you're saying, shifted, is that i should take 25 -14.7 to get about 11.3 or so? or am i way off?
Right click the MAP Gauge display....... go to properties...... change the max = 105kpa to 210kpa....... save. The gauge is default set for a 1 bar sensor.
105kpa = 0psi (if your going by your boost gauge)
210kpa = 15psi (if your going by your boost gauge)
If you want to read the MAP gauge in PSI, subtract 14.7 from the reading on the gauge (if the gauge reads 22psi, subtract 14.7, and your running about 7.5psi)..... this should match up with the Boost gauge
The MAP doesnt display Vacuum like a Boost Gauge does (inches of water or mercury) , it shows Absolute pressure (atmospheric pressure + boost).
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SpeedRacerZ wrote:The MAP doesnt display Vacuum like a Boost Gauge does (inches of water or mercury) , it shows Absolute pressure (atmospheric pressure + boost).
What he means is that on the MAP sensor, 0 is absolute vacuum. Outer space. It doesn't happen in your engine but that's what 0 from the MAP sensor would mean. From there, it goes up.
Your boost gauge reads up and down from whatever atmospheric pressure is at any given time. Generally, atmospheric pressure is just shy of 15 psi. So when your boost gauge is showing 10 psi of boost, that means you've got 10 psi over and above atmospheric pressure in your manifold. That's the equivilant of around 25 psi for the MAP sensor.
Make sense now?
^^^^ thanks, WW.
That explaned a lot for me...
Just to clairfy, the boost guage in my car that also shows vacume, isn't a linear scale. I expected the vacume to track 1 for 1 with the psi, but that looks wrong. The boost side of the guage that is labeled in psi, should track with the map sensor, starting at 14.7 psi, right?
so here is where I was getting screwed up... when I was reading 6psi of boost in the car, the map sensor is reading 105 kpa, or 15.23psi. you subtract the 14.7 from it, and it shows 0.53psi of boost. where am I loosing the other 4.5 pounds of boost?
