I have a 1991 with a 1994 turbo motor. I can't get a tach signal. I tried the resistor trick in the dignostic port and still nothing. What am I doing wrong lol

 

No tach in tunerstudio or dash?

 

Which coils are you using. 94? Or 91? Do they have 3 wires or 4?

 

I'm useing all 91 electornics so 3 wire and on the dash.

 

What did you jump in the diag box.

 

you did the resistor wrong, or you fubared your ignitor.

 

I did the IG- to B+ with a 1/4w 1K resistor. And I've got a brand new igniter.

 

https://www.miataturbo.net/megasquir...already-60744/

 

I read though that. Was slightly confused though. I'm not running cops.

 

What should my tachoutput be in mega squirt?

 

Off.

Wait, if you are still running 1.6 coils and everything the tach should never have broken.

Dead fuse is my guess.

 

Oh ok I'll start checking fuses.

 

Do you have 12v at B+?

 

i wrote a huge reply and lost it explaining why the resistor works and why the tach goes dead when you pull out stock ecu, even though the 90-94.5's tach is driven through coils.

i dont feel like writing it again right now. :(

 

Now I want to know...even on 90-93 with the ignitor?

 

Dang that sucks Brain. Can u sum it up. It's just weird driving the car with no tach lol it's not a fuse.

 

Why does the tach go dead with the megasquirt?

 

because the stock ecu provided the pullup to power the tach signal.

the coils go to ground with each spark event.

the signal must have voltage to start with.

when coils ground, the tach sees constant voltage, then none -- the rate it sees those events is how it knows the engine speed.


1K from B+ (12v) to the tach signal (IG-) puts power back on the wire. otherwise there's no activity on the wire, cause youre going from no voltage to ground -- no signal.

 

Very nice. Thank you brain. I now understand it better. My megasquirt is set to tachoutput should it be off with the resister in place?

 

I don't think the mspnp's even have tach output hooked up. Or at least the jumper shouldnt be set. Adding the resistor is emulating the stock ecu. If adding the resistor isn't working you have bigger problems.