2JZGTE Tacho Feed

[BMWTurbo]

Hi Guys...

I'm still trying to debug my conversion atm. I've stumbled accross a question which I think may help me solve the early rev limit issue.

I am talknig about Pin 16 on Plug A of the ECU, it's often labelled as 'tacho'. I had tried ti use this as my tacho feed (into the tacho) but had no success and ended up using the output from the ignitor to the diagnostics connector which works perfectly.

This prompted me to wonder whether this terminal on the ECU is actually requiring a tacho feed IN rather then supplying a tacho feed out.

Does anyone have any idea on what this is for, and whether it has been used as a feed or an input on other conversions.

The e-manage uses Pin 58 on Plug B for it's RPM feed. As does the Apexi RSM.

[Norbie]

The tacho output on the ECU is a square waveform, which means it's incompatible with tachos expecting an analog signal (eg from an ignitor) which yours obviously is.

[BMWTurbo]

I built the circuit with a coil and transistor to give me a spiked output to drive the tacho. It works fine from the ignitor, but would not work from the 'tacho' Pin 16 on Plug A...

So I was wondering if this particular pin 16 on Plug A required the tacho signal to be 'fed' into the ECU rather then it being the ECU supplying a tacho signal output...

I connected the output of this wire (Pin 16 Plug A) to a CRO and got no real change in it....


I was under the impression that the tacho/Diagnostics wire would only be sending out a square wave output also?

[Norbie]

Hmmm you could be right there. I know I'm using the tacho output wire from my ECU and it works fine; can't recall which pin it was though.

[BMWTurbo]

hrrrmmm thanks anyways Norbie... I just find it a bit odd the E-manage and RSM etc all collect RPM signal from another pin, not the Pin 16, Plug A

[Mos]

I'm pretty sure the tacho signal comes from the ignitor and not the ECU, and it is a low voltage squarewave (the terms digital or analogue I believe are incorrectly used - older signals are still composed of pulses, just at a higher voltage).

Without checking diagrams, the tacho pin you're thinking of is probably one of the communication lines between the engine ECU and the ABS/TRC ECU.

Mos.

[BMWTurbo]

Thanks Mos...

So leaving it 'open' as such shouldn't be an issue.

[Mos]

Without checking, yeah, sounds right.
Mos.