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Speed sensor on FB. I think I may be onto something...

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Old Aug 27, 2020 | 11:44 PM
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Richard Miller
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Speed sensor on FB. I think I may be onto something...
In short, the cruise control on the FB used a speed sensor on the speedometer. a signal is sent out from the cruise control box and ran through the "vehicle speed switch" . It would seem that selecting the Vehicle Speed Input using a DPI with the main source as Drive Train Sensor with Edge Select as Falling and calibrated at the Mazda 1024 pulses@ 60 MPH would provide the ECU with a signal.

That is at least my theory.




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Old Aug 28, 2020 | 07:42 AM
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Cool. Where are you getting the value of 1024 pulse count at 60 MPH?

If you have an oscilloscope or DMM with a frequency count function, you could drive the speedo cable with a handheld drill.
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Old Aug 28, 2020 | 10:27 AM
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From: https://www2.mazda.com/en/100th/
i'm not sure what the signal looks like (i think its an AC voltage? ive never bothered, the ecu doesn't need it), but you're on the right track
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Old Aug 28, 2020 | 11:08 AM
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Mechanical Asian speedos are calibrated to display 60MPH when cable RPM is 1024. So that probably explains the pulse count number you are seeing.
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