compustar 2wssr tach signal

You could also just VMM the wire before doing any changing of wires and see what's going on there.  Make sure you see an alternating voltage less than 1-3 vdc.

...but that wire does not work with the piggy back ecu ...

what is the specific purpose of that piggyback ecu -- does it change fuel/o2 ratios, shift points, throttle response?

yea its kinda semi stand alone ecu that still uses the stock ecu for some things.

that's why i think the wire you are using may not work now -- y'know .. i figured it changes the fuel mixture or something with spark plug timing -- that may be why the compustar does not recognize the signal coming from the tach wire with the piggy back ecu installed.

You MAY only have to reset the compustar brain entirely and RE-LEARN the tach signal without messing with the tach wire connection.  I would try this first as this will likely resolve your problem.  If that does not work, then:

1) reset the compustar

2) install the piggy back ecu

3) vmm a new wire for tach sense

4) re-learn the compustar brain with this tach signal

press the I and II buttons simultaneously for > 2 seconds OR the I and IV buttons sim. for > 2 seconds, one flash of the park lights confirms this step;

next, press the III button THREE times, the park lights in a few seconds will flash rapidly three times to confirm reset to default settings.

Install the piggy back, start the car, let it idle down, now press the tach learn button and see if it learns the signal.

If it does not and again chirps three times, then find another wire.

no, it needs to know engine speed to know if your engine is on or not .. that's why it still needs to know tach/engine rpm.

I think you should just try another wire, shoudl be fine.

Where were you getting the original tach signal?  Did you install a shielded crank angle sensor?  I can't see why the UTEC would mess anything up, unless its a crank signal and you switched signals.

I would tap in to one of the fuel injector wires.  They are right at the ECU.