Tach Signal Problems

[clayw]

I'm running MSII PcB V3 with BG Firmware 2.862 and Ford EDIS ignition control. This is all in my 1976 BMW 2002 with an M10 2L 4 cylinder.

I soldered my tach interface to this diagram:


I used 1N4004 diodes on the pottom and a 1N4742 zener diode at the top. The tach worked for a while, but went dead when it reached 3000 RPM or above. Now it's not working at all. Any suggestions? I've heard of using a resister somewhere in the circuit, but I don't know where.

Any ideas? What am I doing wrong?

Thanks in advance.

[clayw]

Lance,
I tried the IDM terminal first, but no luck. What size resistor would I use?

Thanks!

[Trumpetrhapsody]

Any updates on this issue? I'm trying to build the same circuit, and any time I add the second coil my tach dies. One coil reads 1/3 rpm fine.