MS reads different MAP than boost guage.
 

Hi all, as title states, my MS is reporting MAP values double that of my analogue boost gauge. In ML viewer, I'm apparently pulling 41.3kpa at idle, and my Harbor Freight gauge is reading low 20kpa. My idle is also hovering around 1100-1500, and I'm wondering if this is why. My boost gauge only goes to 30kpa, so it doesn't seem like it's maxing out? Should I trust a Harbor Freight gauge over a MegaSquirt? Anybody else have this problem?

https://cimg0.ibsrv.net/gimg/www.mia...67cfaaf346.png

EDIT: I meant 20inHg, not kpa. So, vacuum guage is reading 68kpa (if the math is right), and MAP sensor reads 41kpa.

Just to make sure - you are converting values, yes? Looks like the HF vacuum gauge has inches of mercury and centimeters of mercury, and boost gauges usually display PSI in boost in in/hg in vacuum.

Just check ambient ms reading with ignition on against a local weather station. That's how I also correct VD runs, to have better/more comparable results.

If it's the same, don't worry about

In the USA, most weather stations publish barometric pressure that has been normalized to sea level, and is not correct for comparison to MAP sensors.

The reported values relate to weather, not to actual barometric pressure.

If your our location in Germany is near sea level, then it would not matter if the reports are normalized, even if German weather stations do the same as USA.

Good info!

I compared 2-3 weather stations with barometric pressure and they're all VERY close, my mapsensor also shows pretty much the same. I'm only 110m above sea level, which helps getting consistent results, I believe ;)

Edit: Yeah, makes sense, they say at these stations "Pressure at sea level". Interesting, doesn't really matter for me, but if you're at altitude, than you can't go after that (logical, there is around 90kpa pressure at ~1000m for example).

Hope he is at sea level :D

EDIT 2:

I have found an AMAZING page for Germany where you can change between ABSOLUTE and "corrected to sealevel" pressure :party:You never stop learning, which is a good thing :)

I'd expect a healthy engine in the 30s, so yes, you may have a vacuum leak, explaining your MAP and high idle, not sure what the rest of your tune is doing though.

:doh:Yeah, forgot that boost guages read Hg, realized in the morning and haven't got a chance to edit my post. I'm pulling 20 Hg at idle, is that normal? According to Google that should be 68kpa, but MAP reads in the 40s.

Thanks, I'll check that out. I'm at work right now, which is right by the pacific ocean, so the forecast at sea level should be pretty close to my reading :). I'll look at that on my lunch break.

Edit: checked, and engine map with ign on is 100.8kpa = 29.76 inHg ~ 30.02 inHg in weather forecast. Glad I can rule out the sensor!

Pretty much just on the base tune, stock VE, stock ignition, afr target on, EGO at 15%, no spark advance, unplugged IAC. Engine idled fine on stock ecu so maybe I introduced a leak in my boost gauge and map sensor piping?