RPM signal to tach for 3.2 DME

[jpahemi]

Does anyone know which wire/terminal is the rev signal on the back of the tach. From what I see on the wiring diagram, it's the green wire to pin 4.
What I'm trying to do is find a rev signal. I'm not sure if I can get this from the neg pole (terminal 1) of the coil; this point seems to go back to pin #1 on the DME.
Thanks,
j.p.

[jpahemi]

Let me try a different question. Those who use the LM-1, how do you connect the rpm cable?
j.p.

[KNS]

I think that the SC tachs and 3.2 tachs are the same in this regard: on the back of the tach there is a connection labeled 'TD'. I think that is where the tach signal goes to.

[Purrybonker]

I'll not be helpful, but I'll get you a bump at least...

I ran a feed directly off the back of the tach and terminate it with a marrette/elec tape under the dash when not using the LM-1. I don't remember which lead/contact it was on the back of the tach, but it seems to me that it was kinda easy to tell which one to plug into once you pull it out. If in doubt just look for the contact that gives variable voltage with changing engine RPM.

My LM-1 varies from the dash tach by about 300-400 rpm, BTW. Nice little side benefit of the LM-1 - allows you to calibrate the dash tach....

[jpahemi]

Purry:
Once I get the LM1 you'll have to explain how to calibrate the tach.
Thanks,
J.P.
Ps. How did you do the 2000 rpm LM-2 calibration if the tach is off?

[Purrybonker]

Actually, I shoulda clarified - the LM allowed me to mentally calibrate the tach. The dash tach is apparently no more a precision instrument than the speedo is and may start to err over time. I'm sure that they can be physically recalibrated - but it probably isn't all that significant with awareness and a chip with an appropriate rev limiter (like the factory chip).

I always used to wonder why I never bumped the rev limiter - the LM illustrated that my tach was overstating revs by about 3-400 near redline. Redline is north of the 3.2 power curve and the G50 has a better gear to offer at that point, anyway.

Have fun with your LM...

[jpahemi]

Purry:
Looks like you can use your PC to calibrate the LM2 rpm cable by having the program emit a signal which represents 2000 rpm's.
Yes??
Regards,
J.P.

[klatinn]

Hi,

Looks like you can use your PC to calibrate the LM2 rpm cable by having the program emit a signal which represents 2000 rpm's.

Exactly. But don't use a laptop computer to do it. Most of them have too weak an audio out signal to drive the RPM converter.

Regards,
Klaus

[jpahemi]

Klaus:
The cable to connect the audio out from the speaker PC will be an audio mini plug directly to the LM1 control unit; correct? Does it matter if the mini plug is a"left and right" type plug? By that I mean it will have a left, right and ground vs. a mono plug.
Regards,
J.P.

[klatinn]

Hi,

Use a stereo plug, not a mono. Also, it does not plug into the LM-1, but into the inductive clamp input of the RPM converter, which in turn is plugged into the LM-1 (that's where it gets its power).

Regards,
Klaus

[ChrisBennet]

I could be remembering wrong but I thought the 3.2L tach wire was black with a purple/violet stripe.

This thread has some scope pictures if that is helpful.
Tachometer pulses per Rev??
Note that the signal peak is ~12.5V. Ignore the voltage you see on the scope channel display.
-Chris