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nmehdikh

current sensing tachometer

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So I've been doing some reading on this, and I want to make sure I got my ducks in a row before I spend money on an adapter.

Car is a 1973 240z, being converted to MS3x 3.57. Factory wiring is gone, no coil etc. Here is a pic of my tach, which if I understand correctly is the current sensing type.

IMG_20180408_151810.thumb.jpg.e3eb9c3734b28221b59984078abcc4f7.jpg

 

I've been reading this thread about using a MSD 8920 adaptor. And here is the manual provided by MSD

So from my understanding there are 4 wires on the MSD box.
1) Ground
2) Tach signal input
3) output to tach
4) violet (unused)

I connect the MS tach signal to wire #2. I take wire #3 and connect it to one end of the tach loop. I connect the other end of the tach loop to a +12v power when the car is running or starting. And I ground wire #1. Will this work?

The other option is using a TM-02-I from technoversions. The instruction manual can be found here.

1) One end of tach "loop" connected to +12V when running or starting

2) Other end of tach loop connected to pin 3 on the tach adaptor (with or without power resistor?)
3) Pin 1 connected to +12V when running or starting
4) Pin 2 connected to ground

5) Pin 5 connected to megasquirt tach output?

Also, on the technoversions adaptor manual, what is the difference between the two +12v sources?


 

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1 hour ago, nmehdikh said:

So I've been doing some reading on this, and I want to make sure I got my ducks in a row before I spend money on an adapter.

Car is a 1973 240z, being converted to MS3x 3.57. Factory wiring is gone, no coil etc.

 

You're on the right path, taking the time to understand the details of how your tach works.  But, there are still coils involved with your MS setup.  I don't know how many, but if it's not one supplying six spark plugs, then it's probably three (wasted spark) or six (COP).  So, the Technoversions unit has the most promise, because if you can set it to a multiple of six, and use it  on one of the single coils, then you can get the tach to read right.  

 

The MSD adapter just conditions the signal for a single coil.  You can't change the multiple it sends to the tach.  It won't work unless you do some trickery.  And it often does not work for people, even on applications it's designed for. 

 

I think that it should be possible to gang the triggers from all of the coils in to one trigger wire and use that for a single coil type adapter.  You'd probably need some resistors and diodes to avoid cross-talk and noise but it should be possible.  I'm kind of surprised that nobody has rigged one up, the concept is pretty simple, the tach needs are well known.  If I had MS I'd send that guy at Technoversions and email and see if he'd be interested in expanding his product line to handle wasted spark and COP.  He'd have a pretty big market, I think.

 

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While posting this I also emailed technoversions with my questions. He's currently looking into the MS manual about the tach signal output, but he believes that the tachoutput signal from MS should be enough to trigger his adapter. If that is the case, it can be wired up similarly to his diagrams.

I'll report back once he gets back to me. I'll make sure to document all of this after I get it working in-case someone has similar questions in the future.

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Brian at technoversions got back to me. I just placed an order for his adapter, and it'll be a couple weeks before I have time to actually wire it up and test it. But this is the general diagram I'm going with. I'll bump this thread with updates later.Capture.thumb.JPG.4a10ca52391242785bf3ea39f26c1877.JPG

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I believe your on ms3x Sequential it would be allot of work to get A  stock z Tach to work is just to switch to the MS tach output from the many spare outputs you have and to a late 280z tach it was fairly easy getting a setup I just did to get his tach to work this way. 

 

But please let us know how it goes as theres always more than one way to skin a cat. 

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I took the guts out of a 280z tach on eBay for 40 dollars and put it in the 240z housing, with 240z gauge plate and needle. Works perfect with my ms2 and cant see a difference.  There is a guide out there for this. Like softtopz said might be other ways but its pretty darn simple.

 

Shane

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