my $2 is on the tacho being driven by the signal going to ground.
in a stock RA40 (18R engine, coil + points), not only is the tacho being driven (tho i'm sure it has it own circuitry) by the coil, but the AC controller is watching that output (wont engage compressor clutch if not running) and a dumb emissions control device that opens/shuts a few VSVs also watches that output to do various things.
the MegaSquirt circuitry expects some of grounding signal (e.g. + rail suddenly going to ground) - either directly off the (-) side of the coil or from the coil- output of some kind of igniter.
Am reasonably sure these things (and similar) are not counting EMF spikes. Most EFI systems go out of their way to filter out coil ringing and other EM interference to reduce false ignition triggering.
... but i'd be glad to be proved wrong (seeing i'm the one who did a film degree last century while you're doing an elec eng. degree)
Sun, 04 September 2005 11:39
