[V8] servotronic connection on 90 V8?

dsaad at icehouse.net dsaad at icehouse.net
Thu Oct 14 13:44:32 EDT 2004

Are you guys sure about this?
I have had a volt meter on this signal while driving. It is a variable voltage
(0 to 12 volts) - proportional to speed. It is not pulsed.
Are you thinking of the speed sender? That is a pulsed signal (the sender is a
Hall Switch), but the output from the speedometer that feeds all these various
control units is most definetly a voltage proportional to speed.
The speedometer is what does the conversion from the pulse train to voltage. In
fact, I am 98.76% sure the speedometer is nothing more than a voltmeter
calibrated in MPH (and the odometer is driven by a small DC motor, driven by the
same proportional voltage).
There are other ways to make an electronic analog speedo/odo, but I am pretty
certain this is how they did it.

For another useless point of reference, the Tachometer works the exact same way.
It receives a pulse train from the ECU, converts it to a voltage proportional to
RPM and sends it to a voltmeter (the tach) calibrated in RPM.

I have no idea what the actual control signal from the servotronic box to the
rack is - but I would have bet money on it being a square wave that varied the
duty cycle to a control solenoid. That would be seem to be a cheap and effective
way to get the job done, but they could have used a linear actuator too.


Quoting DasWolfen at aol.com:

> In a message dated 10/13/04 6:50:00 PM Eastern Daylight Time,
> Steven.Buchholz at kla-tencor.com writes:
> > If you look at the signal getting passed from the speedo you will find
> > that it is actually a pulsed waveform ... so, no, a rheostat providing a
> > variable voltage will not set the boost level ... that is really a
> > bummer ... your idea would have been pretty cool.
>  The speed signal to the controller is a pulsed waveform but the control
> signal to the rack isn't. The key to setting the servotronic manually is to
> determine how the valve is controlled and then installing your setting
> device
> between the stock controller and the rack.
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