Tachometer connection SMC wasted spark

[VE26668]

Hello,

I have a SMC on a 4 cyl engine wasted spark 2 twin ignition coils and 2 ignition amplifiers. Acc to below diagram which I got from MRM I can connect the tachometer using one capacitor and one zener diode out from the amplifiers.

But how big should the zener diode be? Anyone else been trying this solution before?
http://i143.photobucket.com/albums/r141/VE26668/tachoutput.jpg

[gti]

I tried this circuit before. It does not always work.
Your best bet will be to get the tacho adapter from your dealer.

[MRMRacing]

I have not tried this solution but the other with diodes to coil negative. I made up 100 of them earlier but have non left in stock, they work.

[Wroom]

It is worth to mention that the dwell boards for SMC have the possibility to put out a tacho signal at IGN4.
But maybe this tacho out signal is not always connected when the dwell board is installed?

[Chris]

Mitsubishi VR4 engines and some other Mitsu engines have a small module to drive the tacho which is basically two diodes am MRM describes.

Chris

[VE26668]

I have not tried this solution but the other with diodes to coil negative. I made up 100 of them earlier but have non left in stock, they work.

What kind and size of diodes did you use? Zener, Schott etc etc?

[VE26668]

It is worth to mention that the dwell boards for SMC have the possibility to put out a tacho signal at IGN4.
But maybe this tacho out signal is not always connected when the dwell board is installed?

Do you mean to connect the tacho at pin 10? Where in the software do I configure this tacho output?

[Wroom]

Do you mean to connect the tacho at pin 10? Where in the software do I configure this tacho output?
It is not software configured. The tacho out is an output signal of the dwell board.

If the tacho output was wired in when the dwell board was mounted, then the tacho output is there. Should be at IGN4, but could also be at IGN3.

It is the same tacho signal that exist on the PNP units, like for the Mitsubishi EVO.

[Wroom]

What kind and size of diodes did you use? Zener, Schott etc etc?
1N4007 is probably the best.

[blentz2sm4]

i had this setup when i used an SM4, the diode failed on me and it stopped working. I switched to only using one of the ignitors and just changed my tachometer ppr settings accordingly. Also, autometer sent me something to wire in to make the ignitor signal better for their tach - it was free from their tech support people.

[VE26668]

1N4007 is probably the best.

Like this....?


http://i143.photobucket.com/albums/r141/VE26668/Tachoutput_3.jpg

[MRMRacing]

Or like this.....