Second map sensor for baro correction

[dochka]

Hi guys, i've read the MS layout of the v3 pcb about the constant baro correction but didn't understand the point well;
Can anyone tell me what really is the constant baro correction ? Shouldn't the built-in map sensor correct the baro values?
As where i live is a mountain region and i go up and down everyday, i.e i travel from 0m @ sea level to 1800m above that all the time, so any help will be very much appreciated
Best regards

[Bernard Fife]

dochka,

The only time the single MAP sensor can grab the baro reading is just before cranking. It can't use the WOT value, because there may be (and most likely is) restrictions in the intake path, such as the air cleaner, throttle, etc., all of which would indicate to MegaSquirt that the barometric pressure is less than it really is (causing the engine to run worse, not better). However this works fine for most people in most situations.

If you are running up and down mountains, then a single reading at start-up is a lot of use. All you can really do is stop as often as needed to reset the baro reading.

The real solution is a second pressure sensor that monitors the baro pressure at all times and corrects fuel instantaneously. MegaSquirt-II has provisions for this: http://www.megamanual.com/ms2/install.htm#baro, however note this this is one more thing that you may need to tune.

Lance.

[Bernard Fife]

dochka,

I meant to add that the manifold sensor 'corrects' for the intake air pressure, so you are correct on that point. However, baro correction corrects for the lessening of the exhaust gas pressure as you climb in elevation. This lessened back pressure allows more air into the cylinders (for a given MAP), so the mixture has to be richened as you climb and the ambient pressure drops.

Lance.

[dochka]

Thanks mate, i see that it's a must to get the second map sensor
Greetings!