Don't know if it's of any use for somebody, but I added an oil pressure gauge in Tunerstudio. I have a 90-94 ‘real’ oil pressure sender but no real oil pressure gauge in my S2000 cluster (I'm swapping in a S2000 cluster), so I’m using the MS3X to trigger the oil warning light at a preset value. It's not as good as a real gauge, but better than nothing plus I can log oil pressure and exactly choose when to activate the warning light.

The wire coming from the sensor no longer goes to the instrument cluster but to the MS3X on port ADC13 instead. Since the oil pressure sender outputs no voltage (it’s a simple lineair resistor), a bias resistor is added on the MS3X card in the R67 position. The oil pressure sender has a fairly low resistance so I used 330ohm to get good accuracy. Worst case, this pulls about 15mA through the sensor so it shouldn’t be a problem.

The factory manual mentions these values for the oil pressure sender:
0psi = 52 ohm
30psi = 41 ohm
90psi = 16 ohm
That is as good as linear (40ohm would make it a linear curve), so I'm using the 0psi and 90psi values as a linear curve.
Maybe someone with a spare sender could get some real world data.

With a 330 ohm bias resistor we can calculate the corresponding input voltage on ADC13:
0psi : 5*52/(52+330) = 0.68V
90psi: 5*16/(16+330) = 0.23V

With this we can calculate the 0V and 5V values in Tunerstudio:
0V: (90-0)/(0.23-0.68)*(0-0.68) = 136
5V: (90-0)/(0.23-0.68)*(5-0.68) = -864

Enter these values in Generic Sensor Input 1:
sensor – source: Spare ADC (ADC13)
Transformation: Linear mode
0V value: 136
5V value:-864
Lag factor: 15 (need to play with this)

Now you can use a spare output port to trigger the oil warning light when oil pressure goes below 15psi. I use:
Output port IAC2
Power on value: 1
Trigger value: 0
Output channel: sensor01 < 18 Hysteresis 2 (need to play with this)

If you have a real oil pressure gauge, you probably want keep using it (no point in disconnecting a perfectly good oil pressure gauge!). You need no bias resistor and you need to make sure you do NOT send over 5V into the ADC port. The gauge works with 12V, so it’s possible that there's over 5V at the oil pressure sender (I never checked though). If so, you’ll have to use a voltage divider to bring it down to 5V. Obviously, you’ll have to do some math since you’re now using an unknown bias resistor (easy to calculate its value).