Quote:
Originally Posted by jonzobot
Hi t vago,
I have been thinking of this and have a couple of questions about the way the correction is performed in the code.
E.G. - Given that:
a) the MAP sensor in my car has a linear relationship of pressure and voltage; and
b) 1 Atmosphere is roughly 3.6 volts for my particular application;
I was wondering (hoping) this would not need me to make further changes to the code to make the correction factor work better. Is the code flexible enough as written to accommodate differently calibrated MAP sensors?
My disjointed thoughts below:
I have been considering this problem as pertains to my vehicle and I was wondering if the code assumes certain characteristics of the MAP sensors that are specific to Chrysler vehicles? I see for example some numbers in the code for MAP floor, ceiling, and offset - might these values change if we have access to a chart of factory MAP sensor behaviour?
I would think that different manufacturers have different calibrations on their MAP sensors, for instance what voltage constitutes 1 atm of pressure, and the slope of the line (rate of change) of voltage against manifold pressure - if indeed hat slope is linear. Some googling appears to come up with an example or 2 of MAP sensors that vary frequency, rather than voltage for the output to the ECU (this last one is not the case of my Toyota but it may be an issue for some others).
Anyway I would be interested to hear your thoughts on this.
Cheers
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Never really gave it much thought, other than that I never investigated frequency-based MAP sensors for use with MPGuino. I also never considered that any other car manufacturer would implement a returnless fuel system that regulated fuel pressure to a constant pressure above atmospheric rather than regulate fuel pressure based on intake vacuum.
Now, I did make a few assumptions as you mention. One is based on my limited experiences with pressure sensors and their theory of operation, as well as the description of how Chrysler MAP sensors work. So, first assumption was that pressure sensors would generally send out a voltage signal that varies linearly with pressure.
Along with that, I also assumed that voltage-based pressure sensors would have a voltage output corresponding to 0 psia, which would not necessarily be 0 VDC, with a rising slope.
Finally, I assumed that the basic Chrysler MAP sensor would be roughly calibrated, but that manufacturing tolerances would mean that different sensors would output noticeably (but not necessarily significantly) different voltage outputs, given the same atmospheric pressure.
If you had a factory chart that graphed the behavior of your MAP sensor, that'd be good, as I could see whether these assumptions are valid. If not, and if it turns out that your factory MAP sensor does something completely unexpected, like rising as the 4th root of pressure for instance, then maybe instead of trying to tack on more code to MPGuino to handle this exception, maybe it'd just be better to use a separate standalone Chrysler MAP sensor, which only requires +5VDC and a ground.
Clear as mud?