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How to Setup Tacho on Modular ECUs

April 08, 2018

 

The Modular ECUs have a dedicated tacho output pin. This pin is intended for use only as a tachometer function, and can’t be used for generic outputs or engine synchronous functions.

 

 

There is a small inductor built into the ECU to generate a small amount of flyback voltage to simulate an ignition coil, for factory tachometers that require such a signal. So the output is internally pull-ed up to 12V and no external pullup resistor is required.

The only setting that’s required, and this can be found in the functions -> Tacho part in the software, is the output frequency. In the cast majority of cars, the tacho output frequency is the same as the ignition frequency, for example on a 4 cylinder or a 2-rotor engine, the tacho will have two pulses per crank revolution, and an 8 cylinder will have 4 pulses per crank revolution. We give the option in the software to select a different output frequency for cars where this is not the case, and the case of engine conversions.

If you leave this setting set to “standard”, then it will calculate the frequency based on the ignition output frequency (ie, based on the RPM, the number of cylinders and the firing frequency, ie every 360 or every 720 degrees). Otherwise you can choose the number of cylinders to simulate. For example if you choose a 2 cylinder engine, you will have a tacho pulse every 360 degrees.

So, if you were installing a JZ or an RB engine into a Silvia chassis and retaining the factory instrument cluster, you could set the tacho frequency to be 4 cylinder and it would read correctly.

Again note that the tacho output is a variable frequency, and it’s not phase locked to the engine’s rotation.

 

 

Thanks and happy learning!


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