Microtech Lt9-c tach output and factory tacho

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Microtech Lt9-c tach output and factory tacho

Postby orangelancer » Wed Aug 26, 2015 8:47 am

Hey all

car is currently running a 4g63 with a microtech lt9c as the computer and 4 x ls2 coils on the ignition. I want to get the factory tacho to work but the microtech tach output is only 5v. now I've been doing some reading and apparently I need to build an amplifier of some sort???

any help would be great as I would like to get the factory tacho going as all the gauges now work.
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Re: Microtech Lt9-c tach output and factory tacho

Postby Belial » Wed Aug 26, 2015 10:25 am

FINALLY, I can add some value to the site!

The factory tacho will/should be analogue and the system you have fitted will be digital.
You need to get a converter to to run the tacho or change the tacho to a digital one.

Very common issue with the V8 guys, we have factory dashes and then throw in Full ICE/MSD ignitions and hit the same wall.
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Re: Microtech Lt9-c tach output and factory tacho

Postby orangelancer » Wed Aug 26, 2015 10:48 am

so how do I find one of these or make one of these converters? is it an off the shelf thing?
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Re: Microtech Lt9-c tach output and factory tacho

Postby Superscan811 » Wed Aug 26, 2015 11:01 am

All you need is 2 diodes if using wasted spark ie: 2 coils firing at the same time, or 4 diodes if you are individually firing the coils.

Diodes required 1N4007. Pack of 4 from Jaycar is approx $0.80
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Re: Microtech Lt9-c tach output and factory tacho

Postby Belial » Wed Aug 26, 2015 11:02 am

Not sure about the "Microtech" system but have a look on ebay for "Tacho adapters".

MSD make a few different ones as well as other high end ignition mobs.
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Re: Microtech Lt9-c tach output and factory tacho

Postby Superscan811 » Wed Aug 26, 2015 11:10 am

Alternatively, you could use the Microtech output, by simply using a resister and a N channel mosfet.
Jaycar have a N-MOSFET Driver & Output Module for Arduino which will work perfectly for what you want to do.


Cheers.
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Re: Microtech Lt9-c tach output and factory tacho

Postby orangelancer » Wed Aug 26, 2015 2:11 pm

Bought the diodes just the for $0.80c unfortunately every time I go to jay car I buy more than what I came in for :facepalm:

Pretty sure the car is running wasted spark but I will confirm later. If that's the case 1 and 4 fire at the same time and 2 and 3 fire together? correct me if I'm wrong. then ill need to check the wiring diagram to find the original tacho wire from the coil. sounds simple enough hahaha
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Re: Microtech Lt9-c tach output and factory tacho

Postby orangelancer » Wed Aug 26, 2015 11:47 pm

so what earth do I want to be tapping into? the brown ecu or the black engine earth?
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Re: Microtech Lt9-c tach output and factory tacho

Postby Superscan811 » Thu Aug 27, 2015 10:42 am

The Diodes go on the coil negative wire then into the original tacho wire to the dash.
When the ignition is on, the coils should always have 12v running to them, the negative is then switched on and off to fire the coil.
That negative pulse is what the tacho requires to work.

Since you are using wasted spark, the coils fire alternately, so if you just hooked up one of the coil negatives to the tacho, it would read 1/2 of the actual rpm.

If you directly hooked up all coil negatives to the tacho, you would get the correct RPM but it would cause ALL coils to fire at the same time. The Diodes are there to stop that happening.




Cheers.
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Re: Microtech Lt9-c tach output and factory tacho

Postby orangelancer » Mon Aug 31, 2015 1:25 am

So i just drew this up.

Pretty sure this is how my car is wired up. It is running sequential ignition so i'll need to use all 4 dioded. Which wires should i be tapping into? is it the green ones (the ones that run from the ecu)?

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Re: Microtech Lt9-c tach output and factory tacho

Postby Superscan811 » Mon Aug 31, 2015 3:34 am

Microtech Mitsu / 4cyl Wiring diagram. Going off this diagram, the ecu is using a separate "ignitor" module.

Basically, it using a transistor or mosfet as an "electronic relay".
Each coil will alternately be supplied the negative via the "electronic relay" .
That is where you need to tap into. Directly off the coil NEGATIVE.


PS: the diodes will go the OTHER way around..




Cheers.
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Re: Microtech Lt9-c tach output and factory tacho

Postby orangelancer » Mon Aug 31, 2015 8:45 am

the coils have internal igniters. they are a sealed unit.
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Re: Microtech Lt9-c tach output and factory tacho

Postby amgis_obrut » Mon Sep 14, 2015 7:41 am

I run an MT lt16 and run the factory sigma tach of the MT tach out wire
GH Sigma, 16" Mesh wheels, sports steering wheel and a V8 exhaust
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