Inaccurate DFI digital tach readout

[Robert Wilkinson]

When I am driving with the car in gear (standard shift), and the car
is in a steady state condition, the RPM displayed on my DFI will wander
all over the place.  The RPM will be close, but it wanders off as much as
+ or - 75 rpm.  This occurs at all rpm's.  Is this normal with the DFI or
other computers which can digitaly read the rpm signal??  I have 3
different tachometers hooked up to the car, and none of them wander.
FWIW, I noticed the other day on TV that a Nascar using telemetry was
reporting rpm at about + or - 2 rpm.  Also, I recently replaced my pickup
coil and 7 terminal module (gm hei), and the readings were not affected.
And I still have a miss that occurs during light cruising conditions which
I cannot get rid of by adjusting timing, and it may or may not be related
to the DFI problem.

Robert Wilkinson
http://ccwf.cc.utexas.edu/~rw