MAP sensor scaling

merchgod · **Joined:** Thu Mar 30, 2006 2:38 am **Posts:** 5336

I was looking at the map sensor scaling for the 32bit ecus and thinking about adding it to the definitions as I'm in the process of working on a bunch of 32bit defs:

(MAPv * multiplier) + offset

(MAPv * 9.94 psia/v) - 8 psia

I had thought that the factory sensor was supposedly worthless above 22 psig. Based on the conversion above, this would be about 4.5 volts. Does this sound about right? So, it reads up to 27 psig but its accuracy sucks above 22 psi?

Freon · **Posted:** Wed Mar 07, 2007 3:02 am

I'm not sure anyone has actually checked accuracy above 22.5. I haven't seen any actual testing or even heard of someone trying. We do know that it seems to clip output above ~22.5psiG.

Either way, adding the scaling would be nice.

merchgod · **Joined:** Thu Mar 30, 2006 2:38 am **Posts:** 5336

Cool. Will do.

crystal_imprezav · **Joined:** Mon Jul 31, 2006 1:10 pm **Posts:** 48

It is based on atmos pressure as well. Depending on your elevation you will see anywhere from 22.x-23.x psi. I believe it reads up to 36.xx psia max. For me the max I have seen is 23.5 but on my boost gauge it was verified to be 26psi. It will not read above that value since it was stuck at that value while actual boost was above that level.

merchgod · **Joined:** Thu Mar 30, 2006 2:38 am **Posts:** 5336

Right, it is absolute pressure. The 22 psig example was assuming sea level. Sounds like the stock MAP sensor maxes out at 4.5 volts as I don't see any cap on pressure in the code which is actually kind of unusual as everything else seems to have a min, max or both.

themadscientist · **Posted:** Wed Mar 07, 2007 11:07 am

Code:

RPM  MAP MAF
3248  -4.0 2.9  55  10    00   +43.0   13.9 ECU.   -3.4 375.00 2.7  14.22
 3310  -1.2 3.0 102  10    00   +41.5   16.7 ECU.   -3.9 375.00 2.8  15.08
 3356  +0.0 3.1 102  10    00   +41.2   17.7 ECU.   -4.0 375.00 2.9  15.12
 3401  +1.3 3.0 104  10    00   +40.1   18.9 ECU.   -4.2 375.00 2.8  14.58
 3461  +2.3 3.2 103  20    00   +39.6   20.8 +26.0  -4.5 375.00 3.0  13.84
 3542  +2.9 3.2 102  20    00   +39.5   21.4 +26.0  -4.5 375.00 3.0  13.47
 3639  +3.9 3.3 103  20    00   +38.9   23.5 +26.0  -4.5 375.00 3.0  13.42
 3728  +4.7 3.3 103  30    00   +36.6   25.0 +23.0  -4.7 375.00 3.0  13.23
 3840  +5.9 3.6 103  30    00   +33.4   33.6 +23.0  -3.9 375.00 3.1  12.74
 3862  +7.4 3.8 103  40    00   +32.9   37.7 +21.0  -5.0 375.00 3.4  12.17
 4079  +8.8 3.8 103  40    00   +31.2   36.9 +21.0  -5.9 375.00 3.4  11.98
 4050 +10.6 3.9 103  50    00   +29.6   44.1 +20.3  -6.7 375.00 3.5  11.98
 4140 +12.9 4.2 103  60    00   +26.4   48.2 +19.7  -7.6 375.00 3.8  11.92
 4257 +15.3 4.4 103  80    00   +25.2   47.3 +18.5  -9.3 375.00 3.8  11.87
 4415 +18.2 4.5 102  90    00   +23.3   62.7 +17.7 -10.1 375.00 3.8  11.84
 4566 +20.8 4.5 102  90    00   +23.6   68.0 +18.4 -10.4 375.00 3.6  12.02
 4923 +22.9 4.6 102 100    00   +25.7   67.7 +19.5 -11.0 375.00 4.0  12.14
 5035 +23.9 4.8 102 100    00   +27.4   68.9 +20.2 -13.1 375.00 3.6  12.06
 5050 +24.1 4.9 102 100    00   +27.9   65.5 +20.7 -13.1 375.00 3.9  11.98
 5350 +24.1 4.7 102  90    00   +27.2   67.9 +20.5 -13.3 375.00 3.8  11.77
 5537 +23.7 4.6 102  90    00   +27.0   64.2 +20.5 -13.3 375.00 4.1  11.65
 5668 +23.5 4.4 102  90    00   +27.8   67.8 +21.6 -13.3 375.00 4.0  11.62
 5767 +23.5 4.6 102  90    00   +26.9   69.3 +22.1 -10.8 375.00 4.3  11.93
 5847 +23.7 4.7 102 100    00   +25.0   82.8 +23.4 -10.3 375.00 4.1  12.05
 6060 +23.7 4.7 102 100    00   +28.4   75.6 +24.1  -8.3 375.00 4.0  11.77
 6172 +23.9 4.9 102 100    00   +25.1   83.1 +24.8  -8.9 375.00 4.3  11.84
 6265 +23.9 4.9 102 100    00   +26.0   74.4 +24.9  -8.1 375.00 4.2  11.84
 6422 +23.9 4.9 103 100    00   +29.3   87.2 +25.7  -8.5 375.00 4.3  11.81
 6587 +23.7 4.9 103  90    00   +27.6   75.8 +24.7  -8.5 375.00 4.3  11.81
 6802 +23.7 4.9 102  90    00   +29.3   78.9 +26.1  -7.6 375.00 4.4  11.73
 6666 +23.9 4.9 101 100    00   +29.3   82.7 +27.6  -7.5 375.00 4.3  11.62
 6523 +24.1 4.9 102 100    00   +31.8   80.2 +28.0  -7.4 375.00 4.1  11.45
 6858 +24.3 5.0 102 100    00   +32.1   86.4 +28.0  -7.4 375.00 4.2  11.37
 6958 +24.3 5.0 102  90    00   +31.6   87.5 +27.3  -7.5 375.00 4.3  11.34

This is a Utec log with a manual boost controller set to 25psi on a boost gauge. 05 USDM Sti.

TMS

05GarnetLGT · **Posted:** Wed Mar 07, 2007 5:14 pm

looks like its a 2.5bar instead of 2bar....
cool!

WolfPlayer · **Joined:** Mon May 01, 2006 6:15 pm **Posts:** 126

The stock MAP sensor reads 37psi absolute. Subtract your current atmospheric pressure to determine what your limit will be. For me, I am at 14.6 atmospheric. Thus, my max psi is 22.4psi.

t

themadscientist · **Posted:** Wed Mar 07, 2007 9:26 pm

05GarnetLGT wrote:

looks like its a 2.5bar instead of 2bar....
cool!

It is.

TMS

merchgod · **Joined:** Thu Mar 30, 2006 2:38 am **Posts:** 5336

I'm going to add this to the next release.

Also, I'm looking at the multiplier/offset for atmospheric pressure but it is not based on the same input as MAP. I had thought that atmos pressure was determined at startup through the MAP sensor?

crystal_imprezav · **Joined:** Mon Jul 31, 2006 1:10 pm **Posts:** 48

I believe there is a separate sensor that determines atmospheric/barometric pressure.

Jon [in CT] · **Posted:** Thu Mar 08, 2007 12:23 am

crystal_imprezav wrote:

I believe there is a separate sensor that determines atmospheric/barometric pressure.

This is correct and the sensor is mounted within the ECU. If it ever heads south, you need a new ECU.

merchgod · **Joined:** Thu Mar 30, 2006 2:38 am **Posts:** 5336

Jon [in CT] wrote:

crystal_imprezav wrote:

I believe there is a separate sensor that determines atmospheric/barometric pressure.

This is correct and the sensor is mounted within the ECU. If it ever heads south, you need a new ECU.

That would make sense based on what i am seeing. Must be unique to the 32bit ecus as my 02 wrx manual states that the ecu polls the MAP sensor at startup for atmospheric pressure.

05GarnetLGT · **Posted:** Thu Mar 08, 2007 2:08 am

Jon [in CT] wrote:

crystal_imprezav wrote:

I believe there is a separate sensor that determines atmospheric/barometric pressure.

This is correct and the sensor is mounted within the ECU. If it ever heads south, you need a new ECU.

it doesn't just poll a baro read before it starts cranking?

I know 80's turbododges used to do just that;

Jon [in CT] · **Posted:** Thu Mar 08, 2007 2:58 pm

merchgod wrote:

That would make sense based on what i am seeing. Must be unique to the 32bit ecus as my 02 wrx manual states that the ecu polls the MAP sensor at startup for atmospheric pressure.

All 2001+ WRX ECUs have a barometric pressure sensor built in, too. Check out the diagnostic procedures for trouble codes P1110, P1111 and P1112.

RomRaider

MAP sensor scaling

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