How does it know???

KZjim · Post by **KZjim** » Sat Dec 10, 2005 5:34 pm

How do OEM EFI controllers deal with altitude changes? can MS?

PSIG · Post by **PSIG** » Sun Dec 11, 2005 3:02 am

MS can be set-up with dual MAP sensors. One reads the manifold pressure as usual and the other one reading ambient pressure above the throttle blades. It is available for the MS1 versions in the MSnS-Extra code and called MegaBaro <http://megasquirt.sourceforge.net/extra ... ection.htm>. It is also available in the newer MSII as a standard feature with several flavors <http://www.megasquirt.info/ms2/>.

Hope that helps,
David

MiseryQ · Post by **MiseryQ** » Sun Dec 11, 2005 10:20 am

By default MS reads the barometric pressure before the engine is started and uses that info for correction.
Some OEMs do it this way some have a dedicated BARO sensor.

KZjim · Post by **KZjim** » Sun Dec 11, 2005 1:53 pm

Thanks guys... I knew someone could answer my question... Does v2.2 do the barometric pressure check?

PSIG · Post by **PSIG** » Sun Dec 11, 2005 1:53 pm

MiseryQ wrote:By default MS reads the barometric pressure before the engine is started and uses that info for correction.

Good point - I assumed (sorry) that he meant compensation as the vehicle gained or lost altitude while running - rather than just the initial calibration at the given altitude on start-up. MS1 does not compensate 'on-the-fly' in it's standard form.

This was a big aggravation for me when I would cross the mountain passes and have to literally shut the engine off and restart to allow it to acquire the new barometric conditions

Wide-band EGO can correct from a different perspective, but for actual correction based on ambient conditions, two sensors would be required. Am I missing or misinterpreting something?

David

KZjim · Post by **KZjim** » Sun Dec 11, 2005 1:57 pm

OK.. so 2 sensors are requires as described by PSIG.
sensor #1 for ambient pressure and sensor #2 for manifold pressure. Im building a set up for a motorcycle... any ideas on how to accomplish this?

mattuUK · Post by **mattuUK** » Sun Dec 11, 2005 2:18 pm

how about you run Alpha-N an use the Map for compensation?

just another approach...

the other question is: how likely is it for you to have such altitude changes?

I think most of the info is detailed on the -extra site.

regards

Mat

Bernard Fife · Post by **Bernard Fife** » Sun Dec 11, 2005 2:30 pm

KZjim,

It's not clear to me if you have MS-I or MS-II. MegaSquirt-II has the provisions for a second independent 'realtime' baro sensor. This will update your fueling continuously, which may be helpful if you are climbing the Rocky mountains or running Pike's Pike.

To add an independent baro sensor to your MegaSquirt-II, use an MPX4250AP (the standard MS sensor). Run leads from:

- sensor pin #1 (signal) to header position X7 on the V2.2 MegaSquirt main board (JS5 on the V3 main board) through a 1K Ohm resistor,

- sensor pin #2 to ground (the non-banded end of D1), and

- sensor pin #3 to 5 Volts - use the via at the "M" in the copyright notice near the existing MAP sensor on a V2.2 board (use the sanctioned 5V supply in the proto area on a V3 board).

Then set Barometric Correction to 'two independent sensors' in MegaTune.

You can use other 0-5 volt pressure sensors, but you will have to calibrate it using the 'Tools/Sensor Calibration' dialog in MegaTune.

(This is here: http://www.megasquirt.info/ms2/install.htm#baro)

Lance.

KZjim · Post by **KZjim** » Mon Dec 12, 2005 5:09 pm

What would be th best place for the sensors since i have 4 TB's?