Microtech Lt9-c tach output and factory tacho

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orangelancer
Posts: 636
Joined: Sun Feb 20, 2011 10:52 am

Microtech Lt9-c tach output and factory tacho

Post by orangelancer »

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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Belial
Posts: 140
Joined: Tue May 26, 2015 4:40 pm
Location: Melb West

Re: Microtech Lt9-c tach output and factory tacho

Post by Belial »

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.
orangelancer
Posts: 636
Joined: Sun Feb 20, 2011 10:52 am

Re: Microtech Lt9-c tach output and factory tacho

Post by orangelancer »

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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Superscan811
Posts: 1689
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Location: Sydney

Re: Microtech Lt9-c tach output and factory tacho

Post by Superscan811 »

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
Belial
Posts: 140
Joined: Tue May 26, 2015 4:40 pm
Location: Melb West

Re: Microtech Lt9-c tach output and factory tacho

Post by Belial »

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.
Superscan811
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Location: Sydney

Re: Microtech Lt9-c tach output and factory tacho

Post by Superscan811 »

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.
orangelancer
Posts: 636
Joined: Sun Feb 20, 2011 10:52 am

Re: Microtech Lt9-c tach output and factory tacho

Post by orangelancer »

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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orangelancer
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Re: Microtech Lt9-c tach output and factory tacho

Post by orangelancer »

so what earth do I want to be tapping into? the brown ecu or the black engine earth?
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Superscan811
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Location: Sydney

Re: Microtech Lt9-c tach output and factory tacho

Post by Superscan811 »

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.
orangelancer
Posts: 636
Joined: Sun Feb 20, 2011 10:52 am

Re: Microtech Lt9-c tach output and factory tacho

Post by orangelancer »

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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Superscan811
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Re: Microtech Lt9-c tach output and factory tacho

Post by Superscan811 »

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.
orangelancer
Posts: 636
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Re: Microtech Lt9-c tach output and factory tacho

Post by orangelancer »

the coils have internal igniters. they are a sealed unit.
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amgis_obrut
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Location: Orient Point NSW

Re: Microtech Lt9-c tach output and factory tacho

Post by amgis_obrut »

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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