Determining TorqTune2 MAP Sensor Values
CM5-LTS is able to obtain boost readings from any analog 0-5V Manifold Absolute Pressure (MAP) sensor, but it requires the user to provide a few senor-specific MAP Calibration parameters (Slope, Intercept, Atmosphere and Deadband) in order to accurately convert the sensor voltage to boost pressure.
Torqbyte frequently tests popular MAP sensors and publishes TorqTune parameters for those sensor on its website. In instances where the customer wishes to use a MAP sensor we have not yet tested, this blog post will outline the procedure that a customer can follow in order to determine the required parameters themselves.
Before we go further it should be noted that there are two common ways to measure pressure. Absolute pressure reading includes the current atmospheric pressure. Gauge pressure reading does not. So if the pressure was measured at seal level with an Absolute pressure sensor the reading would be 14.696 psi (1,013.25 mbar). If it was measured with a Gauge pressure sensor the reading would be 0.0 PSI (0.0 mbar). The reason this is important to note is that the customer needs to be aware which of the two methods they are using to make the pressure measurements to be used in the procedure described below.
If you have a datasheet for the sensor in question that provides a Voltage vs. Pressure graph for it, you can skip to the example below. Otherwise, read on for a procedure that can be followed to work out the required parameters for any MAP sensor even if if its Voltage vs. Pressure relationship is not known.
Required Equipment and Information
1. A way to measure the sensor voltage. Here you can use a digital multimeter or you can use TorqTune2 Live View Tab. On that tab click [Show advanced data] and observe on the Pressure (V) field just below the [Show advanced data] button.
For this procedure the sensor has to be powered. If using the OEM sensor the engine computer must be powered on. If using the CM5 to power the sensor the unit must have battery power and must have its Orange wire connected to +12Vdc (do not use just the USB power from a connected laptop)
2. A way to pressurize the manifold or at least the sensor by itself. DO NOT use compressed air unless you have an in-line regulator that can limit the pressure that gets applied to the sensor. In most cases a hand pump or a large syringe works best. DO NOT do this with the engine cranking ot running since the engine will be creating a vacuum.
3. A way to independently measure the pressure being applied to the sensor. This could be a standalone electronic or mechanical pressure gauge or a pod-mounted boost gauge or tuning / OBD monitor software. Whatever the method chosen you will need to be sure you know if what you are looking at is showing you Absolute or Gauge pressure readings. You should also be reasonably sure that whatever is used here is as accurate as possible.
4. Current Atmospheric pressure from your favorite weather channel or weather app. This needs to be in millibar (mbar) !!! If it's provided in other units you need to convert it to mbar before doing anything else.
5. A way to relate readings in No.1 and No.3 at the same instant in time. We're trying to determine the sensor voltage at a given pressure. If the way of pressurizing the senor is static (i.e. you can apply some pressure and have it hold) then you can just write down the voltage and write down the pressure. If the applied pressure is rapidly changing you may need to film whatever is measuring the voltage and whatever is measuring pressure at the same time and just pause the video at certain points to capture voltage and pressure readings side by side.
Processing the Collected Data
Step 1: Work out the current Atmospheric Pressure in mbar.
Step 2: Select one "low" pressure/voltage reading and one "high" pressure/voltage reading. Ideally, these should be as far apart as possible while still being within the expected boost range of the vehicle in question.
Step 3: If the pressure measurements were made with an Absolute sensor you already have the data you need. If they were made with a Gauge sensor (like a pod-mounted boost gauge) you need to first convert those readings into mbar then add the Atmospheric Pressure value from Step 1 to each of those readings.
Step 4: Open MS Excel and enter the data collected as follows:
Low Voltage into cell A1, Low Pressure (in mbar) into Cell B1
High Voltage" into cell A2, High Pressure (in mbar) into Cell B2
Click into another cell where you want the TorqTune2 Slope value to be calculated and enter the following formula:
Click into another cell where you want the TorqTune2 Intercept value to be calculated and enter the following formula:
TorqTune2 Atmosphere field should be set to the value in Step 1 multiplied by 100.
Lastly, the Deadband value is the minimum amount of boost (in psi) the engine must generate before the pump tables are allowed to activate. This is an important safety feature designed to prevent pump activation when the engine is off or not making boost. Default value is 3 psi and we recommend you keep it at that.
In this example we'll work out the TorqTune 2 parameters for the 100 psi MAP Sensor we offer as an option with the CM5-LTS kits.
The OEM Part No. of this sensor is PX3AN2BS100PAAAX
If we look up the datasheet for this sensor we can see it includes a graph of Voltage vs. Pressure
We can see that at 0 psi (absolute) this sensor outputs 0.5V and that at 100 psi (absolute) it outputs 4.5V. Converting psi to mbar we get
0.5V @ 0.0 mbar
4.5V @ 6894.76 mbar
We also note the current atmospheric pressure in our area is 14.7 psi (1013.25 mbar)
Now we go over to Excel and enter the following into cells A1, A2, B1 and B2
Using the two formulas above we get Excel to calculate the Slope and Intercept Values for TorqTune2
That gives us our Slope and Intercept Value.
The TorqTune 2 Atmosphere value is just the atmospheric pressure in our area (in mbar) multipled by 100, which in our example is 1013.25 x 100 = 101325
We also decide to leave the deadband at the default value of 3PSI and up with the following TorqTune2 values for this particular MAP sensor:
Finally, click Write to apply these values to the unit. Then click Read, File->SaveAs to save the unit's new configuration so you can go back to it in the future, if required.