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coolant temp, crank signal and speed signal
- Coolant Temp is usually resistance based. So you'd need to measure it on the new ECM as a voltage, leaving it in place on the old, but... then you need to calibrate a range for the coolant temp on the new.. Another way would be to add a second thermistor to the coolant temp for the new.
- VSS and Crank Signals are usually a binary pulse signal - sharing this can be done much like the OBDuino / MPGuino, feed the resulting signal to the control unit (the usual method of operation is for an active voltage to be fed out to the sensor, and the pulses are generated by the sensor closing and opening the circuit, so don't provide the old ECM with two wires, just one, and make sure it's the one that is the 'input' to it, not the voltage feeding out).
Note, I said old ECM in the above, because it's more reliable for the new ECM to have correct sensor data, since it's controlling the engine, the old, only needs that information for the RPM display in the car.
Sharing the VSS though won't *really* be an issue for the new ECM - it's only making economy decisions with it, not critical engine running decisions.
The other ECM might be sharing VSS info with other systems, like the BCM for display data to the instrument panel, but also, ABS / SRS units.
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