Logging crankcase pressure with Map Sensor in InHg.

[karolko]

I have a question about calibrating a GM MAP sensor for an Analog Input sensor that I am planning on using to log my crankcase pressure with.

Now I am familiar on the steps on how to calibrate a regular sensor (AMS-1000, oil-fuel etc), but I want this MAP sensor reading to read in InHG on my logs, not PSI or kPa. is that possible?

Would I have to just do a conversion from PSI to kpa to InHg or what?

 

[norbs]

Yes its possible, rename the sensor name, and you will need to know your values of your sensor in HG vs volts not psi vs volts, so convert your readings for psi into HG. Then use those values for the calculations.

1 Kpa = 0.145037738 Psi

1 PSI = 2.036" of Mercury (HG)



looks like for a 1 bar gm map

0 Hg = .3 volts
29.6 hg = 4.9 volts

 

[karolko]

So the in my my log, when the crankcase is pressurized i will see POSITIVE InHg and when i am pulling Vacuum i will see NEGATIVE InHg? Is that correct?

If that is true, then when we say that the call pulls 8 InHg of vacuum at idle, it really means -8 InHg? Correct?

If so then it all makes sense.

 

[Duts87ss]

If using a 1-bar MAP like mentioned above, you will only be able to read when the crankcase is in vacuum.

 

[HighPSI]

Sorry Adrian, been in Illimois tuning. When using a 1 bar MAP to record crankcase pressure the approximate values are Gain= (-6) & Offset= (30). This will display you value in inches of Mercury (i.e. vacuum). Obviously, you can hook a vacuum pump up and get the values exact for your sensor, but these will get you in the ballpark. The values will get larger as vacuum increases.
FWIW: They actually have these values listed as the default values for "Pan Vac (InHG) in the Analog Sensor section.