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JM_S2

Porsche 944 S2 tach signal

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I bought supercharged S2 few month ago.  It  has i44 ecu and it works fine except rev counter.  Tacho is enabled from the settings but the needle doesn't move.  Is it possible that the signal from the ECU is too weak for the original tachometer?  Installation is made by finnish firm which sells these products and they couldn't sort that problem (according previous owner).  Original Moronic sends 12V square wave to rev counter.  It is not hi-level rev counter which would be connected to the negative side of the ignition coil. Do i need pull-up resistor or other kind of amplifier between i44 and rev counter?  

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Hi JM_S2,

The standard link/vipec tacho out is a 12V square wave so I would have expected it should work.  The only thought I have is that maybe your tacho requires more current than the ECU internal pull up can supply.  I would try splicing a 100ohm pull-up between 12V and your tacho signal wire and see if that works.

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Yes.  I connected signal wire directly from vipec to tacho terminal and draw ground and positive wires directly from battery.  Tested with original tacho and even bought other 100% working unit which doesn't work either with vi-pec.  That doesn't leave much choice.

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Check the tach settings. There is a multiplier make sure this is set to 1 not 0

You can also do a test pwm on the drive.  Changing the frequency will change the tach reading.

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Multiplier was set to 1.  Tried with 100 Ohm pull-up resistor. Still no life in the meter.  My friend took a sample with oscilloscope from his 944 turbo (with Augtronic) and his tacho works fine.  Can anyone verify is this signal is similar to a signal from Vi-pec?

951RPM.jpg

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Should be very similar to that. Looks like about a 30% duty cycle in that capture.

 

Should be very similar to that. Looks like about a 30% duty cycle in that capture.

 

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