Here is a summary of the connections I made to the factory E36 sensors.
The RPM signal is a clean 12V pulse train who’s frequency is proportional to the engine speed. If you setup a rising edge interrupt and a timer, it is easy to measure the signal’s period. Be sure to scale the 12V appropriately for your devices I/O levels. It gives one pulse per cylinder fire and there are three pulses per rotation so the equation boils down to:
So RPM = MeasuredPeriod(micros) / 20000000(micros)
The RPM signal can be found at three fairly convenient locations that I know of. The wire is always solid black:
- Pin 1 on the round diagnostic connector under the hood on the passenger side
- Pin 20 on connector X16 to the back of the gauge cluster
- Pin 8 on connector X22 to the cruise control module behind the glove box
The Speed signal is also a clean 12V pulse train who’s frequency is proportional to the vehicle’s speed. Be sure to scale the 12V appropriately for your devices I/O levels. The sensor is in the rear differential and outputs 9 pulses per revolution.
Speed = 6313.13 * TireCircumference / MeasuredPeriod(micros)
The Speed signal is black with a white stripe and can be found on:
- Pin 2? on connector X16 to the back of the gauge cluster
- Pin 10 on connector X22 on the cruise control module behind the glove box
- Pin 10 on radio connector
The TPS signal comes form a potentiometer mounted on the throttle body. It’s middle pin/wire outputs 0-5V proportional to the throttle position. Note that there is about a half a volt of deadband on both ends resulting in an effective range of about 0.5V to 4.5V. I ran this into an ADC and scaled to provide a percentage.