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Old 09-25-2011, 06:08 PM   #1
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Default ems 4 tach setup

im curious how to get the factory tach to operate using aem software and any hardware setups needed to complete the setup.
I have a 94 miata running on ems4
Im using k series honda cops
and a modified optical wheel
custom harness and all that fun stuff
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Old 01-02-2013, 09:15 PM   #2
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I also need help on this wiring. I have a '00, Ive looked at the factory wiring diagram, it shows the stock tach basically connected to a black box. The black box has some inputs from the PCM.

Does anyone know which stock PCM connections drive the tach? Is it a straight connection from one of the EMS GPIOs to a wire on the instrument cluster to drive the tach? Is it a 12V pulse, 5V? I'm guessing it's the Green/Orange wire that connects to pin 2K going into the PCM. It also routes to the Data Link and transmission control module.

Last edited by adamvs; 01-02-2013 at 09:50 PM.
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Old 04-05-2013, 11:26 AM   #3
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It depends on which Miata you have but once you locate the wire that leads to the tachometer (in the cluster) you basically need to apply a pull up resistor to drive the 12v tach signal. The AEM EMS4 will only output pulsed ground.

1. Go to the tab Tacho/Speedo (might be a hidden tab) - Find the free GPIO or the GPIO you're using for your tach output. Lets for example say "GPIO 7" and make sure you change the "TACHO OUTPUT" field to this output, GPIO 7.
2. Attach that GPIO wire to the tachometer wire going to your cluster.
3. Tap in your 2.2k resistor and then run that to a switched 12v source (ignition).

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