In article ,
NY wrote:
"The Other Mike" wrote in message
...
In article ,
Bill wrote:
What I wish I could find again was the online lecture by some
American who had delved into his Jeep's ECU and demonstrated that,
for example, the rev counter was not driven directly from sensors,
but via lookup tables whose inputs combined info from more than one
source. If I remember correctly, he deduced that the rev counter was
more of a driver comfort display rather than direct reality. So you
can't trust any of this stuff.

Can't think of a reason for the rev counter not to be in effect
directly driven.
Rev counters and indeed most dash gauges including speedos nowadays
are either driven by stepper motor or are a visual widget on an LCD
display.

Quite possibly. But, irrespective of how the signal reaches the
dashboard and how it moves the needles on the gauges, I'd still expect
the feed for the gauge to be from a crankshaft rotation sensor that is
also used for determining timing of fuel injection and (for petrol)
spark. Likewise I'd expect the speedo to be driven from a
wheel-rotation or final-drive-rotation sensor. I suppose you could
drive the speeo from a GPS receiver and give a true reading, but you'd
still need the wheel rotation as a fall-back in case of loss of GPS.

Doing it any other way seems unnecessarily complicated.

Point I was making was that I can't see any reason why you'd want a tach
to read anything other than true engine RPM. No point in fitting one
unless it's reasonably accurate. After all a rev counter is of zero use to
many drivers. For those who can make use of it, needs to be reasonably
accurate.

--
*It's o.k. to laugh during sexŒ.Œ.just don't point!

Dave Plowman London SW
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