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Severely Erratic Speedo Reading


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DI 2 assigned to GP Speed 1, then GP Speed 1 assigned to both Driven & Driving Wheel Speed.

I'm getting severe fluctuations on the speed readings - reaching 5000+ km/hr. :blink:
In between the big fluctuations, smaller ones I can probably filter by using Math function (average) - but the big fluctuations would still affect the computed average.

Is there a way to filter ridiculously high frequencies being picked up by the DI? I don't have an oscilloscope to confirm at what frequencies the big fluctuations come at. I tried grounding the speed sensor on different locations. I even used shielded cable which made no difference.

On the log, I'm using a reed switch speed sensor from gauge cluster (speedo gauge driven by cable). I also have tried to use a magnetic/hall effect sensor with magnets placed on propeller shaft. Both of them pick up the same high frequency noise.


*vehicle on jack stands - reason why TPS % seems low. :lol:

Maybe I'll try to make a simple low pass filter circuit with parts I got at home.

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I have made a passive RC low pass filter (diagram below) for the GP Speed 1 input, made a math block av (as GP Speed 2), and had been assigned to both Driven & Driving Wheel Speed. Wheel speed readings now seem useable - I just need to find the correct calibration (I have to compare by GPS).





@Adamw I know I read somewhere before where you mentioned the DI falling voltage to be considered by the ECU, but I can't seem to find it anymore. Should it falling below 1.0v or 1.5v?
I just want to make sure so I can try to make fine adjustments on the frequency cut-off by changing the values of the resistor or capacitor. :) 

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