MicroSquirt.com read only forum (Jan.15,2018)

im having a tough time getting my microsquirt to read rpm. it's a fuel only install on a waste spark ignition system. using only one coil, the optoin- is connected to the 12v constant side, the optoin+ is connected to a diode and 1kohm resister in a Y pattern - the diode to the switched side of the coil harness, and the resistor to the 12v constant side. i'll run a datalog, crank the bike, and get no RPM.

am I wired incorrectly? i've tried having the VR1+ connected to 12v, still nothin. does the optoin+ need to go directly to the switched side of the harness?

thanks for the help. ive tried searching and ive followed other threads, but still nothin.

Your description isn't completely clear - which direction is the diode pointing? Please see the attached drawing for something that has worked for a lot of people. One thing that may have to change - you have +12v to OPTO-; this is a very low-power set up, without the spikes that make feeding Vbatt necessary. Just connect OPTO- to ground.

hey thank you for the quick reply.

the banded end of the diode is facing the coil. I wired it according to that diagram initially (matt's), and received no rpm input either. My wiring is exactly the same, minus the connection to coil 1&4. i'll try grounding opto-. im guessing that if I did not use the diode and resistor, then supplying 12v to opto- would be necessary?

thanks again. ill give it a shot

sikowanalize wrote:if I did not use the diode and resistor, then supplying 12v to opto- would be necessary?

That's right, and probably 24-36v worth of Zener diodes as well. Everyone who's used it has commented on how it's astonishing just how clean the signal from this circuit really is.

awesome - connected opto- to ground and it read RPM. the fuel pump relay kicked in as soon as I grounded it - tunerstudios showed a rpm jump, scared me half to death haha. but I cranked it over and it's reading RPM. you may be right about needing to take a signal from both coils - which is odd to me, you think when you select fuel only and waste spark, MS would automatically double the valve for two coils.

thanks again

When you have Fuel Only selected, 'Wasted Spark' means nothing to the uS. It isn't an input setting, but rather an output setting, selecting how many times does the uS pulse the ignition triggers per cycle.

If this is a twin, drive off of one coil - you'll get two fuel squirts per 720* engine cycle. If this is a four, drive off both, and 4 trigger pulses = 4 squirts per cycle.