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Looking into getting a new EMS and after some research I can't seem to find a definitive answer. All I've seem to have found is people saying hondata is good to make your car do one thing and it'll do it well. I'm thinking what if I get my car tuned then move somewhere with a significant elevation change; will I have to pay to get it tuned again or will the ECU understand the change via the MAP sensor and alter the fuel maps on the fly to compensate?
 

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There are corrections in the oem ecu hard code that use the baro sensor for reference. It can also be used for calculations related to fuel pressure and engine load, etc. Since the MAP sensor can only read in absolute, it has no idea what the ambient pressure is at any time other than when in key on/engine off, which is a rare state that typically only happens once a drive cycle. Without a baro sensor the ecu can only get this data once and if ambient pressure changes much during the drive cycle the ecu can't compensate. You also need to consider that the speed of sound varies with atmospheric pressure, and this has an effect on the engine of changing the VE and shifting the torque peaks up and down the RPM range a bit. This will cause error in the fuel maps (and the timing maps). High end/motorsport ecus and OEM calibrations compensate for this shift by adjusting the map breakpoints depending on baro pressure.

It's a little muddy on exactly what the obd1 ecus are correcting but it makes sense that it's part of the fueling corrections, and especially so since these ecus are using a pulsewidth based strategy instead of VE based. I will say that, since I lose about 1500ft driving from where I live/tune to the city/beach/airport that I can see the baro sensor is working by looking at the data. I used the s300 lambda mode closed loop and have spent quite a bit of time tuning with it to get it working really well. If I drive from here to sea level with the baro sensor active, I have very stable and low fuel trims at all times. If I uncheck the baro sensor box in SManager, I then have some learning up as I head south and learning back out as I head north.

But if you are staying at a fairly consistent elevation, you may not notice even if you are only running open loop. I would suggest that you tune as close to sea level as you can, and hit the entire map. When you are at elevation you just won't make it all the way up to the WOT line, but you should still be fairly well tuned there. It's the same as tuning the entire boost region of the map on a boosted car as opposed to just doing the full boost column and interpolating down.
 
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