VersaTune User Forum

You can try doing some math by hand:
MAPPressure (kPa) = MAPVoltage * Multiplier - Offset
For your sensor multiplier = 65.7777, offset = 5.4444
The MAPPressure that should be displayed at 0.9V is 0.9 * 65.7777 - 5.4444 = 53.76 kPa
That is even lower than atmospheric pressure at 101 kPa indicating a vacuum condition. It does not make sense that the cars max out at that.
MAP voltage is read by the ECU directly from an analog to digital converter. Its scaling is not editable, so the voltage should be pretty accurate.
Perhaps it is a different MAP sensor with a different scaling. Maybe it is faulty.
Does the voltage graph have a normal shape that resembles your boost graph with stock sensor? Does it flatline at any point or show inverted behavior (boost should increase, but voltage decreases)?
You could try connecting an external boost gauge and compare the readings.

Hi Ugnius

Thanks for the reply. When I noticed the low value last night I did the calculation and noticed kPa values of around 50kPa. It seems as if the voltage flatlines yes.

Hi Ugnius

Please see the comparison of boost(bar) vs map voltage in the attached image.

I'm wondering if you could mock something up to connect the MAP sensor into some pressurized housing and measure the voltage.
I've had this sensor and I remember the highest value it read on my car was 309.8kPa or something (about 30PSI, even though above 29.5PSI of boost the results were kind of weird). So unless the sensor is damaged (it happens) or the wires soldered wrong these sensors should have a pretty consistent response curve from 0.9 to like 4.8-4.9V or so.

Hi there. Thanks for the reply. We had the owner of the car in question switch the wires around. We found the 2 diagrams online and compared them. Seemed as if they were switched around. After testing the results where the same. But now the AP and onboard bosst gauge does not read boost. Interesting though when he tested the voltage with the harness not plugged into the sensor it was reading 1.25V, as soon as its plugged in the voltage drops below 1, like 0.20V.

Does anyone have the scalars for the Bosch 4BAR sensor, part# 0281002576?

I tried to calculate them but I'm missing some knowledge. If I use the formula: then I get the offset - 3.7037038 and then scalar A* scalar B = 92.5925925 But because I have no relation between A and B I can;t extract them further even if I basically have 3 ecuations they are present in (for the minimum reading of 50kPa at 0.5v, 100kPa at 1.04V and 413kpa (60psi) at 4.5V.

I've got the data from here: https://www.efihardware.com/download/13 ... -Datasheet

It doesn't matter what A and B are as long as their product is what you need (92.5925925).
So you can use A=92.5925925 and B=1

Awesome, thank you!

225 and 2.43 looks a lot better, it divides cleanly with only 2 decimals.
so 225 with 2.43 and offset of - 3.7037038. WIN.

A and B are multiplied by the ECU, not divided. You should check your math.