MAP sensor problems... bigtime.

[SovXietday]

Hey guys, just moved to Hondata from Crome.

I'm running a standard GM 3 Bar 122223861 sensor. It worked just fine for me with Crome.

I set the car up with the MSD dropdown menu for their 3bar, when I fired the car up it was reading 24"vac while my boost gauge clearly read 19-20". Then, as I was driving around I would get to 2-3 psi at half throttle just to pop off, but the MAP tracer was still over 14 and sometimes 10" vacuum?!

I turned the car off and turned the ignition on. Checked the MAP sensor voltage, 1.39. Well that would explain why it's so off.

I've done a ton of calculations, none of which matched up correctly to what my car was running. SO, I fiddled with the settings until atmospheric pressure was 1.39V and 5V was 31.1psi. There was NO change at all to what the MAP tracer was doing. I hit full boost once just to see if maybe it would bump over... definitely built boost (APEXi AVCR read .71Kpa)

According to the datalog, at full boost the car read -2.1" vac and decided that 33* of timing was necessary. :?

Can someone help me fix this issue, I know the MAP sensor is working just fine but I can't figure this out in the slightest. :(

[Spunkster]

MAP Scalar and Offset
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Here is how to calculate the scalar and offset for a MAP sensor.

1. Find the minimum and maximum voltage and absolute pressures.

2. Convert the pressures to mbar.

3. Subtract the minimum and maximum voltages to find the range, then do the same for the pressures.

4. Divide the pressure range by the voltage range to calculate the scalar.

5. Multiply the minimum voltage by the scalar to calculate the offset. Note that a positive voltage gives a negative offset.



Example for a 3.5 bar MAP sensor:

1. For a 3.5 bar data sheet:
0.5V @ 0 kPa (absolute)

4.5V @ 345 kPa (absolute)



2. 345 kPa = 3450 mbar.

3. Voltage range = 4.0V, pressure range = 3450 mbar.

4. 3450 / 4.0 = 862.5 = scalar

5. 862.5 x 0.5 x -1 = -431.25 = offset

So scalar = 862, offset = -431

Plug in the minimum and maximum voltages to check your work:
0.5V x 862.5 - 431.25 = 0 mbar @ 0.5v

4.5V x 862.5 - 431.25 = 3450 mbar @ 0.5v



If you have trouble then draw a graph and extrapolate the lines until they cross the pressure axis.

[SovXietday]

Thanks, I was being an idiot last night. I did that calculation but never tried it out as it didn't match up to the readings I was getting.

After calculating.

Scalar - 628
Offset - 0

Worked like a charm. :)