Joes:
a lot of the cars had a hall sensor looking at a steel trigger wheel for the engine rpm, so i thought these might be the same
They probably are the same, but those other cars you're thinking of aren't using Hall effect sensors either.
You need to measure the voltage level over the range of speeds you need to support when the sensor is installed. You will almost certainly need to do some signal conditioning to take your variable voltage incoming signal and clean it up to a square wave.