stand alone ECU but i want to keep my rev clock

[jondee86]

Nomuken Wrote:In my case I have a 20V with coil on plugs, so no coil negative to get
my tach signal. Haltech generates a tach signal nut my OEM rev counter
doesn't understand it. So I still got no revs Any thoughts?

Just going thru this exercise with my own ECU. It seems that when the
the factory tacho is driven from the ECU (as it is on the AE86), then the
signal from an aftermarket ECU may not be compatible for driving the
tacho... without some help.

EDIT: Above is not correct. After more research it becomes plain that
the ECU tacho connection is an input not an output. The tacho signal is
in fact generated by the igniter. And it will be a back EMF voltage spike
rather than a square wave.

In my case the tacho output is provided by a spare ignition output... this
is set up to pull 12V to ground. So the answer is to put put 12V onto the
line from the tacho to the ECU output by way of a 560 Ohm "pull-up"
resistor. When the ECU switches the 12V to ground, the result is a 12V
square wave on the tacho wire.

Haven't got it wired up yet, but if the original OEM ECU feed to the tacho
was a 12V square wave, then it should work fine

EDIT: Above solution is discarded, as a 12V square wave will not work
for the AE86 tacho. New solution is to use a small pullup coil instead of a
resistor, to generate a voltage spike. Wil post up the results after I get
back from vacation

Cheers... jondee86