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thisismatt

ECU tachometer signal

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Working on wiring for a VQ35 and thinking about tachometer signal.  Since the VQ's all typically use a canbus system with a combination meter control unit, this becomes a bit confusing when hooking up a traditional tach.  There's one output from the ECU that assists with the power steering system called engine speed signal.  I can't find anyone referencing this signal in other VQ swap threads.  The FSM gives the following waveforms and I'm having a brain fart trying to determine if this is suitable for a regular tach, since I'm not clear what type of signal the tach needs.  This seems to indicate that the signal will have 6000 pulses a minute at 2,000rpm - is that correct for a 6 cylinder tach input??  I know the voltage may be too low for some tachs...

 

enginespeedsignal.jpg

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6000 pulses per minute is correct for a 6-cyl 4-stroke engine at 2000 rpm.   (2000 rpm is 1000 pulses per cyl, x6 gives 6000).

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On the VQ35 like the SR20 there is no "RPM" wire. According to the manual the engine speed signal is also used for fuel cutoff at high idle. Funky shit going on there with multiple inputs, might not be the best tack signal.

 

I don't know what tack you have, but I used a coil trigger wire to run my Speed Hut Revolution Tack. I just had to tell the tack how many cylinders there were. 

 

Looks like your cylinder 1's coil trigger wire is yellow and red, pin #62 coming out of the ECU. 

 

Make sure to disconnect the battery, and Good Luck!

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There is a pin 103 off the ecm that goes to the power steering control, that's what I'm referring to. It's not documented very well, but the waveforms I posted are off that wire.

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Battery is... disconnected :D

 

IMG_20180610_190410.jpg

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Ha, The entire car is disconnected.  :lol:  

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Those waveforms are a 5V signal, so that won't work for a traditional tach.  You need a 12V signal.  

 

You may be able to modify a 4-pin HEI module to transform that signal into a tach signal by hooking the waveform and a ground to the input terminals (both wires from the crank trigger), then add power to the module and use the tach terminal for your signal.  

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From what I've seen I should be able to use a pull up resistor of around 10k or 12k to make that work

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