hook up your laptop/scanner and watch your MAP sensor then convert kPa to inHg.
Sort of. Not exactly.
A vacuum gauge measures pressure DOWN from atmospheric pressure--which varies with altitude and weather, but for ease of mathematics and memory, I'd say equals 30 inches of mercury, or 1000 millibars.
A MAP sensor measures pressure UP from ZERO. Zero in this case is the inverse of atmospheric pressure.
IF (big IF) atmospheric pressure at your location really was 30 inches (check your local weather report) and the MAP sensor shows 20 inches, you've got 30 - 20 =
10 inches of vacuum. If the MAP sensor shows 12.36 inches of pressure, the vacuum gauge would show 30 - 12.36 =
17.64 inches of vacuum.
Here's a conversion chart I quickly downloaded, there are other more detailed ones on the web.
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I would expect the scan tool to be programmable to read in American units instead of Metric. But maybe I'm wrong.
At any rate, that's a more-useful-than-usual chart, in that it converts
both the metric/American units AND the pressure/vacuum. 100 kPa of
pressure = 0 inHg of
vacuum, etc.
So the scanner would be a step....Possibly a vacuum gauge would give information the scanner won't if still on the search for answers?
No. There's nothing a vacuum gauge connected to manifold vacuum can tell you that the MAP sensor connected to manifold vacuum can't, if you process the MAP sensor signal into something recognizable.
A decent scan tool should be able to graph both crank position and MAP sensor signal, so that
you can watch the MAP sensor signal in relation to each cylinder's intake stroke. A vacuum gauge won't react that quickly, AND you have no way to correlate it to the individual cylinders.