DIYPnP Tach not working (MX5/Miata 95.5)

[Varnish]

Running a DIYPNP on an MX5/Miata NA8 (1995)
Running Firmware V 3.4

Just hooked it up and started debugging, and the first big bug is the tacho on the dash isn't working.
TunerStudio displays the rpm fine.
I have turned tack on and off and on again in TS, and set the speed to half speed, normal and back again.
Nothing.
I have Tach output connected to pin 4i, and have checked the continuity.

What else can I try?

[Varnish]

I've looked a bit further into this, but still don't have a solution......

Apparently these engines either came with 3 wire or 4 wire coils.
If the coils have 4 wires the tacho takes its signal from the ignitor.
If the coils have 3 wires the ECU provides the signal for the tach.

The fix for a 4 wire coil is to put a 1k resistor across pins -ign and +B in the diagnostic port.
The fix for 3 wire coil is to enable the tacho in tuner studio.

I have the 3 wire coils, and the tuner studio fix doesn't work.
I tried rewiring the Tachout from 4i to 4L but that didn't work either.

[Matt Cramer]

Check the tach output voltage in output test mode. It should give you 12 volts when off and 0 volts when on. Does it?

[Varnish]

Hey Matt
I'll try that as soon as I get the chance.

I've also built and tried the circuit below:

http://msextra.com/doc/ms1extra/MS_Extr ... VTacho.GIF

I tried it with the output to 2i and 1F. No dice

The stock ECU has 2 plugs if that makes any difference.
When I switch back to the stock ecu and the tach works fine.

[Varnish]

Check the tach output voltage in output test mode. It should give you 12 volts when off and 0 volts when on. Does it?

Matt I get 6.5v off and 0 volts when on.

[Matt Cramer]

Try running a 470 ohm resistor from 12V on the DIYPNP to Tach and see if that helps.

[Varnish]

Thanks Matt.
I appreciate the support. Especially as this is a diy low cost product.

I've got 2 questions:
1) isn't that circuit that I tried pulling the voltage up to 12v already?
2) If I connect 12v to the tach, where do I connect it? Straight to the tach pin?

I'm sorry, my electrical knowledge is pretty poor and most if this ecu stuff is beyond me.

[Matt Cramer]

Yes, but it may need more current.

[Varnish]

I finally had the opportunity to put the 12V feed on the Tach pin this weekend.
No response from the dash tach.

Are there any other options for getting a tach signal?
Like taking a signal from the coil or building an external Tach signal circuit?
Has anyone done something like this?

[Matt Cramer]

What voltage does it put out now when the output is turned off?

The 3 wire coils do not supply a good tach signal, and I've never seen one of these cars need an external circuit.

[Varnish]

I disconnected the transistor circuit and put all the wiring back to stock.
Now I see 11volts at the tach pin with the output switched off, and 11 volts at the tach pin with the output switched on.

Could I run the tach off one of the spare injector outputs run through that transistor circuit?
I guess I'd need a large resistor to pull down the amps from the injector output?

[Varnish]

Well

I make a new transistor circuit triggered by a spare Injector output.
Verified it was all working. I don't have a scope, but my multimeter has a frequency function which roughly tied up with the rpm in tuner studio.
Pulled the dash apart and put the signal wire straight into the back of the tach.
Nothing

I'm not sure what my options are now, after market gauge I guess.

[blackice]

Hey Matt
I'll try that as soon as I get the chance.

I've also built and tried the circuit below:

http://msextra.com/doc/ms1extra/MS_Extr ... VTacho.GIF

I tried it with the output to 2i and 1F. No dice

The stock ECU has 2 plugs if that makes any difference.
When I switch back to the stock ecu and the tach works fine.

Hey Varnish,

I got mine working

- No circuit required ....

Tach out to pin 1F, turn on tacho in tuner studio.

Hope it works for you as well !

Dave