DIYEFI.org Forum

This should work, if at all, on a naturally aspirated engine only. Why do we need two separate sensors, one for MAP and one for barometric correction? With just one sensor:

1) Record barometric pressure on power up (everyone does this).

2) At pre-determined intervals, check if TPS = WOT

3) If TPS = WOT, record MAP sensor reading.

4) If New sensor reading deviates "X" ADC from power-up ADC, update the barometric pressure value.

Does this sound like it could work?

This will work, but only at low rpm unless your engine is very very well setup :-)

Also, things like air filters etc will start to mess with your baro correction over time.

It's a good thought though.

I'm a sea level kinda guy to be honest, so it doesn't concern me all that much, but I do go skiing, so I need to take more of an interest at some point :-)

Thanks :-)

While I spent more time at WOT than most people I know, I really don't think most people spend enough time at WOT to make this work even if you saw TRUE unmolested atmospheric pressure at WOT which as mentioned above - very few people do.

But it was a good thought!

GartnerProspect wrote:While I spent more time at WOT than most people I know

Sounds like you might drive similarly to me ;-)

I like having two sensors. It would be great to have a realtime barometer on my dash display

That said, what Subaru does/did is switch a solenoid to change pressure sources every once in a while and use a single sensor.

Dodge did constant baro correction with one map sensor on their turbo cars from 85-93.. They used a simple 3way vacuum solenoid.. When the time was right, it would switch the map sensor to the open port on the solenoid, it'd see atmospheric air pressure, then it'd switch back. It did this VERY fast, and I belive it did it right after snapping the throttle shut on a decel event. It takes a bit of extra code, but is by no means difficult to do. They used the same solenoids to do this that they used for boost control, EGR, evap..

Interesting technique :-) Thanks for sharing guys!

That IS interesting.

Funny too considering you'd still need another I/O from the processor to control the solenoid, and I can't imagine solenoids are much cheaper than MAP sensors.

GartnerProspect wrote:That IS interesting.

Funny too considering you'd still need another I/O from the processor to control the solenoid, and I can't imagine solenoids are much cheaper than MAP sensors.

My thoughts exactly. The only reason I can think of is the lack of available ADCs.

first, I would like to know what everyone here understands as "barometric correction". True 'correction' would be to adjust the barometric reference to fudge the fuel calcs for some complexity that we are not taking into account in the basic fuel calculation, I would think. One thing that MS2/E and, I think, base MS2 code can do is barometric reference load calculation. This makes the most sense to me. If the fuelling code shows errors at altitude, for example, this can be adjusted, but without referencing the barometric pressure for load, I cannot fathom how you may be able to 'correct' load for altitude. In MS2, they refer to this as '% baro'. Basically, it is map/barometer. If this is done at power up or continuously is academic. As for the cost of a freescale MAP sensor that does not have a port for connection to a hose, they are cheap and easily sourced. If you do not want to a) use an ADC port to read it out or b) buy a sensor, you can use the barometric reading at power up. This calculation of map/baro reflects the change in efficiency of discharging the exhaust to different pressure reservoirs as well as the ability to pull from this reservoir. If this calculation needs minor trim we could add a 'correction' table, but I think this should be the basis for the calculations. A consult of the Heywood bible, I think, will show this. I'd pull mine out, but it is buried in the basement, currently.

http://www.amazon.com/Internal-Combusti ... 007028637X

Gearhead