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biyanpian
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Joined: 02/24/2015 - 08:06
MAP sensor reading

Controller:  EMS-4; Engine:  Toyota 2ZZ-GE;  MAP sensor:  3 bar supplied by MWR with kit

With details posted above, my MAP sensor is reading engine load at 1.81 Volts, 1.2 PSIg, with the engine off, using a base map provided by the vendor.  Presets are: Min Volts 0.2, Max Volts 4.8, Load Offset 2.000, Load Scalar 3.000, Filter 6 Teeth.  Is it possible to tune the MAP sensor reading to correctly read 0 PSIg without throwing off the rest of the map?  If so, how?  Load Offset?

AEM_NS
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Last seen: 5 months 2 weeks ago
Joined: 06/06/2014 - 09:31
It'd be helpful to know the

It'd be helpful to know the sensors actual calibration; ie, what voltage equals what pressure.  I wouldn't blindly start adjusting things until it reads some value that you think it should be.  If you unplug all other sensors and leave the MAP sensor plugged in, does the MAP reading change?  

biyanpian
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Last seen: 3 years 5 months ago
Joined: 02/24/2015 - 08:06
The part is AC Delco 12592525

The part is AC Delco 12592525.  Apparently it's a GM/Cheverolet performance 3 bar sensor, which should have an approx. linear output, based in this info (chart shown is for a 2 bar, scaling to 29.4 PSI).  Now, at a slightly higher elevation, reading flickers between 1.78 and 1.79V, giving a reading of 0.9 PSIg engine load with the car off.  Before, it was giving a voltage reading of 1.81 with a reading flickering between 1.1 and 1.2 PSIg.  Input voltage at the sensor reads 4.99 from power pin to ground, with everything (all sensors except the MAP sensor) connected.

I haven't had a chance to disconnect all other sensors, but will do so if a fix doesn't present itself that doesn't require doing so.  The engine seems to run perfectly on the factory ECU, and the only other sensor which is connected to the EMS-4 is an O2 sensor which doesn't seem to have any faulty wiring (voltages read correctly).

Thanks for your help.

AEM_NS
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Joined: 06/06/2014 - 09:31
Eh, I think your best bet is

Eh, I think your best bet is going to be to re-calibrate the sensor yourself.  On that page you linked to there is a chart for GM 3Bar MAP sensor but I have a feeling its for the old school style MAP sensors and not the new style you have.  According to the data, a 3Bar sensor has this transfer function: v*8.94-14.53 for psig which is actually v*62.28+3.6 for kpa.  The correct settings for this calibration are min=0, max=5, scalar=3.114, and offset=3.6.  I tested these settings and they work perfectly for the above calibration.  Atmospheric pressure (101kpa) should be 1.56 volts.  You're seeing about 1.80v at atmospheric which tells me your sensor does not follow the calibration data from the web or the calibration given to you by MWR. The MWR settings would show 101kpa as 1.68-1.69 volts.  

You'll need to figure out the sensors min and max voltages and the pressures at those voltages.  Once you have that data (real empirical data and not just bad web data), we can help you with the right software settings.

biyanpian
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Joined: 02/24/2015 - 08:06
Thanks for the heads-up.  May

Thanks for the heads-up.  May I ask how to generate the formula once sensing range, output voltage at 0 PSIg, max voltage, min voltage are known?  For instance, it now seems (assuming the part is functional) that this is a 3 bar sensor, and its output voltage at 0 PSIg for this part is 1.81v (I am at 10 feet above sea level and getting that reading). Once I have minimum voltage and maximum voltage (by applying vacuum and pressure), what do scale and offset represent?  Is scale simply the slope of the line, and offset the "y intercept", for instance?.. or does one of those represent a curve in the output voltage?  As an example, what would be scale and offset for this sensor if minimum output (at -14.7 PSIg?) were 0v and maximum output (at 29.4 PSIg?) were 5v, since the 3 bar range and 1.81v at 0 PSIg (at sea level), if you don't mind saying?

Thanks for the help.  I hope to be able to test for min and max tomorrow.

biyanpian
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Using a pressure gauge (with

Using a pressure gauge (with a vacuum pump, followed by an air compressor) which reads from -30 inHG to 60 PSI, and which is supposedly accurate to +/- 1%, I gathered the following voltage output readings (using AEMtuner).  I might need to run a second set of tests (and consequently submit corrections), but I want to get this to you with the hope that proper calibration values can be generated with this data as a starting point.  Voltage min is obviously 0.31, and max is 4.71.. output range is apparently 4.4 volts rather than the 4.6 shown in the base map.  We were having a high-pressure day and are near sea level, so actual atmospheric pressure was higher than 14.696 PSI (as indicated).

To save me some time figuring it out, would you mind briefly explaining the math of how you went from:   [v*8.94-14.53 for psig] to [v*62.28+3.6 for kpa] to [min=0, max=5, scalar=3.114, and offset=3.6]?  Since 1 bar = 100 kpa, I assume that the scalar (3.114) is the full range, in bar, of the sensor.. If that is correct, the explanation of the first step would be most helpful (going from v*8.94-14.53 to v*62.28+3.6). Thanks!   edit:  For the sake of clarity, I know that the values I mentioned above are not correct for the sensor I have.. I am simply trying to understand how to convert from the first set of values to the second for any set of data, so that I can know the scalar and the offset.

I will check the below values later today and will try not to bug you with further questions about MAP calibration values if I can understand the above conversions.

 

0.31     min V out

0.38V    -28 inHG    0.94 Abs. PSI
0.48      -26            1.93
0.58      -24            2.91
0.69      -22            3.89
0.79V    -20 inHG    4.87 Abs. PSI
0.89      -18            5.86
0.99      -16            6.84
1.10      -14            7.82
1.20      -12            8.80
1.30V    -10 inHG    9.78 Abs. PSI
1.41      -8             10.77
1.52      -6             11.75
1.62      -4             12.73

1.82V    1 atmosphere [*conjecture*, 29.92 inHG (14.696 PSI)]
1.84V    atmos. press. [local, 30.21 inHG (14.84 PSI), 65 degrees F]

2.03V    2 PSI       16.696 Abs. PSI
2.14      3              17.696
2.25      4              18.696
2.36      5              19.696
2.47      6              20.696
2.57      7              21.696
2.68      8              22.696
2.79      9              23.696
2.90V    10 PSI      24.696 Abs. PSI
3.01      11            25.696
3.12      12            26.696
3.23      13            27.696
3.34      14            28.696
3.45      15            29.696
3.55      16            30.696
3.67      17            31.696
3.78      18            32.696
3.88      19            33.696
3.99V    20 PSI     34.696 Abs. PSI
4.10      21            35.696
4.22      22            36.696
4.33      23            37.696
4.43      24            38.696
4.54      25            39.696
4.65      26            40.696

4.71V   max V out

AEM_NS
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Joined: 06/06/2014 - 09:31
Give this a shot: min=0.40,

Give this a shot: min=0.40, max=4.65, offset=9, scalar=2.68

This should work well.  I verified it on a test bench.  Your raw values are a little wonky as they're not entirely linear so there is a little bit of a compromise but the difference across the sensors entire range is pretty minimal.  Assuming these settings give you appropriate readings, you should probably let MWR know that this new school "GM 3Bar" MAP sensor (which is really a 2.8Bar sensor):

...does not equal this 25 year old "GM 3Bar" MAP sensor:

biyanpian
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Last seen: 3 years 5 months ago
Joined: 02/24/2015 - 08:06
Thanks for the numbers and

Thanks for the numbers and for confirming on the bench.  I noticed that the numbers weren't completely linear, and am going to do another set of tests to see if/why they were off.  I just received this pressure gauge.  I'll definitely be letting MWR know.

Would you be willing to briefly explain how to convert the PSIg formula to kpa?  In the above example [v*8.94-14.53 for psig], [v*62.28+3.6 for kpa], [min=0, max=5, scalar=3.114, and offset=3.6], I know that 62.28 is derived from (8.94 x 6.9), that the scalar is the range (in bar) represented within the min and max V range (slope).. just not sure how the kpa offset is calculated, which is a critical part of the calibration.  The only thing I see is the odd 14.53 value, but 14.7-14.53 = 0.17 PSI = 1.17 kpa.  Where does the 3.6 come from?

Thanks again.

AEM_NS
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Last seen: 5 months 2 weeks ago
Joined: 06/06/2014 - 09:31
The equation I posted is the

The equation I posted is the mathematical slope and intercept for the same sensor scale but in kpa instead of psi.  Scalar is total scale in percent (basically kpa) over 100 and offset is min sensor reading at min volts.  

Sometimes it's just easier for us to do it. smiley

biyanpian
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Last seen: 3 years 5 months ago
Joined: 02/24/2015 - 08:06
Thank you for the calibration

Thank you for the calibration values.  I tuned the fuel map shortly after you provided them, and the car has been running very well ever since.

Soon I'll be adding a supercharger (low boost) and larger injectors. :)

zazzn
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Last seen: 3 years 1 month ago
Joined: 08/30/2015 - 23:56
Hello, I've been trying to

Hello, I've been trying to figure this out for a Greddy pressure sensor that comes with the Profec boost controllers. There seems to be lists onine for the voltage to PSI. Is there not an easy way to just adjust a cal like the IAT sensor in the AEM pro software?

 

https://www.google.com/search?q=greddy+pressure+sensor+voltage&espv=2&bi...