This function provides a 0-12V pulsed output to drive a low-level tachometer from an auxiliary output pin. There will be one output pulse for each spark plug firing, therefore the frequency of the pulses is determined by the engine speed. The tacho duty cycle is adjustable to cater for the requirements of different tachometers.

 

Note: The tacho drive will NOT trigger high-level tachometers which are designed to be run directly from a coil's negative terminal.

 

The tacho output can provide calibration correction and a key on sweep feature.

 

The following adjustments configure the tacho drive:

·Max RPM - Sets the maximum engine speed that the ECU will display on the tacho, this is often required when an older vehicle has been fitted with a higher revving modern engine. A value of 0 results in no limit being applied, the Multiplier and Offset need to be set correctly for this max rpm to be visually correct.

·Multiplier - Sets the correction of the output frequency of the tacho in relation to engine speed. Normally this value is set to 1.0, resulting in one tacho pulse per ignition event. Tacho Multiplier can be used to calibrate tachometers that do not read correctly or when a tacho is used on an engine with a different number of cylinders from which it was originally designed for.

·Offset - Used to correct inaccuracies in the tacho needle's installation, this value adjusts the position of the needle by a constant offset throughout the entire range. Note this setting requires the Multiplier to be correct before the offset value can be treated directly as an rpm value.

·Tacho Duty Cycle - The percentage of time that the tacho output will be driven low. Therefore a higher duty cycle will give longer pulses than a lower one. There will be one output pulse for each spark plug firing, therefore the frequency of the pulses is determined by engine speed. Adjustment of this value may be required to get some tachometers to operate correctly.

·Key On Sweep - Activates the key on tacho sweep feature. This feature causes the tacho to sweep round to the Sweep RPM at key on then back to 0.

·Sweep RPM - The maximum RPM the tacho will sweep to at key on if Key On Sweep is enabled.

·Sweep Time - The time taken to reach the Sweep RPM.