Yep, I found that tach and tried to learn something from it. Actually,
I think the reason its reading different from the front has something to
do the reverse polarity of one of the plugs. When I reversed the wires at
the coil, the readings switched. Either that or for some reason the energy
coming from that side of the coil is stronger. I think I might adjust my
design to sense all the pulses at the coil of a vehicle. That way I won't
have to worry about trying to keep one wire isolated. Pretty easy to do in
code. I just have to tweak my antenna.


 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

If you're measuring engine RPM, it's actually an asset to have an
ignition
that fires with every revolution.  There's a commercial tach Here:

http://www.tinytach.com/tinytach/gasoline.php

that sounds like what you're doing.  I suspect the front cylinder is closer
to
some source of interference - perhaps the coil - that is
generating a second
pulse with every spin of the engine.

"The government cannot give anything to anyone that they have not first
taken away from someone else."