Hello,

I am looking forward to do a PowerDyn setup (http://www.powerdyn.fr/English/PowerDyn.html) on my car.
This is a low-cost dyno-like system, that gives a rough image of performance changes between different setups.

All you need is to get a tach signal and send it to your laptop's line in (or record it with a MD or MP3 recorder, then process it on your desktop computer).

A suggested setup is like this:

The signal is taken from the negative terminal on the coil, which gives an inverted signal.

I would like to grab the signal from the ECU harness.
I've had a look at the schematics there: http://miataturbo.wikidot.com/ms2-h.
I also found this, which seems to be for a 94+ NA:

2I would be perfect, but on MT's NA schematics it is not connected on my 91' NA.
So far, I see:
- 1G ou 1H, it seems connected to the negative coil terminal. What do you think of it? Does it seems OK to you?
- 2E (CAS). This wire seems sensitive to perturbations. I don't feel confident in connecting there.

Thanks

 

Ever heard of the diagnostics box?

it's even labeled IG-.

 

Yes, but it's on the engine compartment, and I'm lazy on finding another path through the firewall to the passenger's side if I can avoid it

 

There is a little unused grommit on the passenger side that you can punch a hole in and have a professional looking device and a free hole to stick your goodies in.

 

Back of the instrument cluster, position 1H, a yellow / blue wire:



That's the tach signal. 0-12v squarewave.

 

That's right. Very easy to access, very clean. But I already have my vacuum tube for the Megasquirt in

Great, I like this proposal!
So I guess I could set my voltage divider between 1H and 2J?

 

If it's convenient for you, then yes.

 

OK, so I did it with a 10Kohms (series) and a 470 ohms (parallel with line in) to reduce the signal to around 1/20th.
It gives a Line-in compliant 0-0.6V squarewave that PowerDyn can process.