CodingParadox
New member
So I tried to do this mod yesterday. I tested the leads on the turbo pressure sensor, and found that the wires didn't quite match the colors in the writeup on alltrac.net, but figured that at least the function of the 3 wires would be identical if I could figure out which was which. So I found out that brown is ground, one of them (I believe the orange with a blue stripe?) had constant +5v, and then the middle one (something with white and dotted with blue) had about +2.4v with the car off (0 vacuum.)
So I figured the middle on should be the PIM, right? Sure. Well, I took a 10k pot and hooked it up in series with that line, and found something very odd. There's higher voltage on the ECU side of the line than on the sensor side, so the voltage on that lead is also coming _from_ the ECU. Also, making sense with that, the more I raise the resistance, the _higher_ my turbo pressure sensor goes.
So I'm semi-baffled with that. But in any event, the next problem is how to properly do this. It would seem to work to put the pot across the +5v lead, because then I'm scaling the input voltage, which should scale the output voltage as well, it's just odd both that this method didn't work and that the writeup explicitly says do it to the variable lead.
So I figured the middle on should be the PIM, right? Sure. Well, I took a 10k pot and hooked it up in series with that line, and found something very odd. There's higher voltage on the ECU side of the line than on the sensor side, so the voltage on that lead is also coming _from_ the ECU. Also, making sense with that, the more I raise the resistance, the _higher_ my turbo pressure sensor goes.
So I'm semi-baffled with that. But in any event, the next problem is how to properly do this. It would seem to work to put the pot across the +5v lead, because then I'm scaling the input voltage, which should scale the output voltage as well, it's just odd both that this method didn't work and that the writeup explicitly says do it to the variable lead.