Now that we can finally drive our 1971 Super Beetle, we need to program the VDO electronic speedometer so we know how fast we're going.
Now, going in, all we knew was the advertised revolutions per mile of our 205/40R17 tire was 860.
We didn't know how many pulses per revolution the Holofex sensor and the EMPI electronic speedometer cable sends out and the instructions didn't say.
We get our VDO speedometer into programing mode by starting with the key in the ignition but turned off.
We press the button on the face while the key is off and continue to hold the button while we turn the key on.
We can release the button as soon as we see pulse.
Pressing the button repeatedly, it will show adjust, auto cl, and then goes back to pulse.
Since we don't know what the pulse reading would be, we toggle to auto cl so we can do an auto calibration.
After a few seconds, button will display.
We press the button again and start will appear and flash.
While start is displayed, we want to drive a measures mile.
Using a GPS speedometer app on our phone, that has an odometer readout, we drive a measured mile and we stop.
We press the button and we get a reading of P13,910.
The needle will do a full sweep and go back to 0 and is now programed.
If the speedometer reads P00, you pressed the button before driving or you may not be getting a signal from your inductive sender so check the wiring and repeat the process.
After the fact, knowing the readout of 13,910, we can do some math and figure out how many pulses per revolution the speedometer sender sends so you can use the advertised rollout of your tire.
We divide the 13,910 pulses by the given rollout of 860 revolutions per mile of our tire and we get 16.14.
So, the EMPI inductive speedometer sends out 16 pulses per revolution making our actual rollout 870 revolutions per mile.
That assumes 100% accuracy from our GPS speedometer app.
Knowing that, we could set the speedometer using the pulse method.
With the speedometer in program mode, we would stop pressing the button as soon as pulse is displayed.
After a moment, the display will show the factory set number or in our case, the auto calibrated number.
Noting the first 0 can't be changed, as the second number flashes, pressing the button cycles through the digits.
Say we wanted to use the advertised rollout for our tire, 860x16=13,760.
So, we would set the second digit at 6, wait for the third digit to flash, set it to 7, and so on.
Once we have our number entered, we can release the button, wait for the speedometer to flash through the remaining digits, the needle will do a full sweep, and now it's manually programed.
Either way we programed our speedometer will give us a very accurate measurement.
The adjust feature requires a chassis dyno with a speedometer readout and if you have access to one, it could be used to further fine tune the speedometer.
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