Hi Piemmm

The Turbo on my 2010 Mazda3 2.2 liters diesel, following manufacturer specs, can boost up to 1.8 bars (that means about 280 kpa).

What happens using MAP to calculate boost is:

when pressure on the manifold goes over 255 kpa the reading goes crazy, the indicators tilts between positive and negative values.

I know that there’s some restrictions on min/max PID values and teorically is not possible to measure values over 255 kpa from map sensor, but…

…today I’ve done some test to understand why the indicators tilts between positive and negative values instead to stay @ 255 kpa, and I’ve found that follows:

On my car when MAP pressure go over 255 kpa, so 256 kpa Torque (and not only torque) reports 0 kpa, instead to show 257 kpa it shows 1kpa, instead to show 258 kpa it shows 2 kpa… and so on like on a follows:

so the tilting behaviour is explained, when real pressure excedd 255 kpa, and value in bar are shown negative: 0 kpa = -1 bar, 1 kpa = -0.99 bar and so on.

Here some graphical examples obtained from log recordings:

In blue the boost pressure calutated with MAF method, in red the boost calculate with MAP method, the green dotted line is the real pressure in manifold (I’ve put the values manually transforming 0 kpa to 256, 1 kpa to 257 and so on).

and here: http://digilander.libero.it/ctectr/torque/Mazda3%20Boost%20Pressure%20Analisys.xlsx the xcell file with some othe data.

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So what I’m asking you is if you can add a new boost calculation mode in way to show boost from MAP when the pressure goes over 255 kpa.

Maybe You can name it “Experimantal MAP for high boosted diesels” or something like that, trasforming low values like 0, 1, 2, 3 … to 256, 257, 258, 259…

For info, the lowest pressure meausered on my car intake manifold was = to 50 kpa during a filter regeneration, so teoretically for diesel engines you could transform values from 0 to 49 kpa as 256 to 305 kpa (that means it can be possible to measure pressures till to 2.05 bars)

I know I can do that using MAF or ALT methods, but using MAP the readings are smoother and more accurate: most of times pressures till 0.3 bar are not reported on low acceleations, the indicator moves only on heavy/modearte accellerations.

Could you do that?

Tell me if I can help you in some way

another little up… 😀

do you think is feasible to add a new boost calculation method based on map sensor that works in this way:

if map pressure >50 kpa and < 256 kpa, boost (in bar) is = to (map pressure - baro presure) /100 if map pressure >0 kpa and < 49 kpa , boost (in bar) is = to ((map pressure + 255)) – baro presure) /100 ________________ let me know… for me shold be useful to read pressures over 255 kpa (so 1.55 bar) via map sensor.

Test pid 0170 for a response. It may
have your boost embedded in the data
returned.

Edit:

Boost
Header: 7DF
Mode/Pid: 0170
Equation: (((B*256)+C)*0.0048346)-Baro()
Units: psi

Without the test response I am guessing
at the variables.

Ok, I sorted out this issue creating a custom pid using this equation:

A+256*(1-((24-A)&256)/256)

The second part of the equation allows to have value 1 from 25 to 255 kPa, and value 0 from 0 to 24 kPa.

In other words we have as result A+256 for values of A between 0 and 24, and A+0 for values of A between 25 and 255.

@burro thanks for the hint but I dont obtain any response fro 014F pid 😉