First, I am admittedly not much of an electrician. I am installing a new MT09 engine in my new to me Legend car and the MT09 cars do not run tachometers, because there is no output for one. The MT09 is a euro only (I think) 970 ish cc three cylinder.
The street bikes with this engine do not have a tach either. But the car is so snaky that I would kind of like to have a big red shift light to remind me where I am at. I tried to find an ecu pinout but failed, but the community claims even if I could find one it would not give me a tach signal. So I thought of tying into an injector, but I have an idea there would not be one clear signal per revolution. I do not know how injection is managed on one of these motors but thinking it is perhaps pulses that change with RPM? (Around 11,500 max depending what I read.)
There is no external shaft for a hall sensor either. Just the geared output shaft.
Anyway, looking for suggestions.
The ECU must be getting a cam or crank signal to know how fast the engine is spinning at a bare minimum, finding and tapping into that signal could be an option.
If that's not an option, the least tricky solution might be to add a magnetic or optical trigger wheel somewhere, it could be as simple as a silver-painted section on the crank pulley with an optical sensor bolted to the block to pick it up. There are a lot of dirt-cheap modern aftermarket tachs that run from a 5-12V square wave signal.
It could also be possible to run from something that makes a pulse every 2-4 rotations (edit: or even every 1/2 rotation) with the proper signal multiplication, which some aftermarket tachs have onboard. The biggest problem with running from an injector might be that the injectors could cut off under engine braking, it's a standard feature on production car ECUs.
There are inductive tachometers that just clip on a plug lead.
I believe some are even fancy enough you can program a multiple for number of cylinders or 2 stroke versus 4 stroke.
They aren't spendy--
https://a.co/d/90XdNvj
Isn't the old school way to just tap into the spark plug or coil wire?
Karacticus said:
There are inductive tachometers that just clip on a plug lead.
I believe some are even fancy enough you can program a multiple for number of cylinders or 2 stroke versus 4 stroke.
That sounds simple. I'll go dig into that idea thank you.
In reply to Karacticus :
I considered that option but it looks like the MT09 uses CoPs, so the only high-voltage signal to pick up on would be in the spark plug tube...
In reply to GameboyRMH :
There's a trigger for the COPS, probably switched ground. There's your signal.
In reply to Keith Tanner :
Yep that was my next thought. The only issue might be that some ECUs cut spark along with fuel on engine braking, but it's a better option than an injector signal at least.
Oapfu
HalfDork
1/19/25 2:52 p.m.
This is supposed to be a shift light compatible with MT-09, does it work for you?
https://www.healtech-electronics.com/products/slp/
Actually, it's a universal-fit kind of thing. The installation instructions show splicing into the ECU harness, so presumably that's an RPM signal of some sort.
I was expecting something more 'elegant' like reading CAN messages. There are adapters from the Yamaha diagnostic plug to OBDII, and there are dataloggers that supposedly work with MT-09, so presumably you also should be able to get real-time data that way. Yeah I know that if someone has not already figured it out, CAN-sniffing is not 'just' hook up a reader and go.
From an AEM datalogger, the different options for MT-09s
You guys are mostly talking Greek. But the shift light has potential since that is really what I want. Thanks for that. By the way, any guages must be analog so inductive tachs appear to be ruled out.
The MT09 should absolutely have a tach. It's likely digital, but virtually all bikes - particularly sporty ones - will have a tachometer.
bearmtnmartin (Forum Supporter) said:
You guys are mostly talking Greek. But the shift light has potential since that is really what I want. Thanks for that. By the way, any guages must be analog so inductive tachs appear to be ruled out.
Inductive can totally be analog. It's just a way of reading a voltage pulse in a wire.
Keith Tanner said:
In reply to GameboyRMH :
There's a trigger for the COPS, probably switched ground. There's your signal.
And playing with that was how I fried an MSPNP trying to make a 90 Miata tach work with a later PNP.
Just because it's COP doesn't mean you can't remotely mount a coil with a plug wire.
In reply to Pete. (l33t FS) :
1.6 Miatas aren't COP, but they do have a separate ignitor module not found in the later cars. There's some weirdness about the 1994 cars as well. Later NBs were semi-COP with just a relocated coil running two plugs. But there's still a trigger.
In reply to Keith Tanner :
This was a Mazdaspeed Miata engine/harness and MSPNP. Ask EvanB for the details, as it was his car that I broke, but there was some issue with this engine and that chassis and the other computer that meant there was no off the shelf way of using the tach.
I was poking around the coil trigger wires with a Power Probe trying to see what did what and then the engine stopped running and started being a statue 
The crazy part is that he then lent me another one of his cars to drive at Nationals.
Keith Tanner said:
bearmtnmartin (Forum Supporter) said:
You guys are mostly talking Greek. But the shift light has potential since that is really what I want. Thanks for that. By the way, any guages must be analog so inductive tachs appear to be ruled out.
Inductive can totally be analog. It's just a way of reading a voltage pulse in a wire.
What I meant was I see nothing available.
Pete. (l33t FS) said:
In reply to Keith Tanner :
This was a Mazdaspeed Miata engine/harness and MSPNP. Ask EvanB for the details, as it was his car that I broke, but there was some issue with this engine and that chassis and the other computer that meant there was no off the shelf way of using the tach.
I was poking around the coil trigger wires with a Power Probe trying to see what did what and then the engine stopped running and started being a statue The crazy part is that he then lent me another one of his cars to drive at Nationals.
If I do anything similar I have to send the ECU back to US Legends for reflash or repair. Considering the INEX name of the series stands for inexpensive, they are very good at extracting cash from car owners.
In reply to Pete. (l33t FS) :
Weird, because those cars have a nice tach signal wire in the harness. IIRC it comes off the coils but it's been a while since I was digging around in there. That's the semi-COP, it's really just normal batch fire coils with two of them mounted on top of spark plugs.
For this application, I'd be looking at how tachs were handled on old cars that didn't have any electronics or hall effect sensors and had a wiring diagram that fit on a business card. Tachs aren't fundamentally complex.
I expect I will go with the Healtech shift light. It is a simple dummy proof installation and will do just what I need. You can program a series of colors to show rpm ranges which would be a lot easier to see peripherally than a gauge anyway. Thank you for the suggestions.
