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Thread: How does a tacho sensor work?

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    Administrator AB's Avatar
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    Noob question but I'm very intrigued how a tacho sensor works?

    I now have a td42ti model which had an exposed dimple in the timing gear area as opposed to an indent on the td42, is that correct?

    Apparently only the td42ti model had that, why?

    I had to put a spacer on my tacho sensor for it to work and just curious if anyone knows how that actually measures and why the TI model was changed?

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    Patrol Freak jff45's Avatar
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    The sensor is a magnet so it works as an inductive pickup. My TD42T reads approx. 1v AC on idle and increases with speed.
    The tacho is a type of voltmeter so reads accordingly.
    The non Ti cam gear has holes so the metal between the holes provokes the signal. I don't know why they used dimples on the Ti. Also don't know what signal it puts out but I suspect it needs to be a bit more precise for the ECU.

    My original signal was from the toothed gear of the IP but it ran through the EGR electronics that were used on the Safari.
    I wasn't able to use it with my TB45 tacho so I had to mount the normal sensor on the timing cover and use a Dakota Digital tacho interface.
    John

    2001 GUII TI 4500 - Now converted to TD42T auto with Nomad valve body

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    AB (25th November 2016), mudski (25th November 2016)

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    Patrol God mudnut's Avatar
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    Crank angle sensor explained https://www.youtube.com/watch?v=RuIislTGOwA There is not a lot of info around for the engine revolution sender.
    Last edited by mudnut; 25th November 2016 at 05:07 PM.
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    Patrol God mudnut's Avatar
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    This should shed some light on what to look for.
    Attached Images Attached Images
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    Patrol Freak jff45's Avatar
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    That only covers the mechanical pump TD42. I don't know if the TD42Ti with electronic timing control and the dimples on the cam gear puts out the same signal. I've read several conversion threads where they haven't been able to get the tacho working with the Ti signal.

    It also doesn't cover the TD42T mechanical pump with EGR which reads off the IP gear

    @AB what tacho do you have working with the spacer under the sensor on the dimpled gear?
    John

    2001 GUII TI 4500 - Now converted to TD42T auto with Nomad valve body

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    Administrator AB's Avatar
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    Quote Originally Posted by jff45 View Post
    That only covers the mechanical pump TD42. I don't know if the TD42Ti with electronic timing control and the dimples on the cam gear puts out the same signal. I've read several conversion threads where they haven't been able to get the tacho working with the Ti signal. It also doesn't cover the TD42T mechanical pump with EGR which reads off the IP gear @AB what tacho do you have working with the spacer under the sensor on the dimpled gear?
    The original 1990 td42 GQ one mate. It works fine but doesn't read below 900rpm.

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    Patrol God mudnut's Avatar
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    Can you swap it with another to see if the Tacho is ok?
    My advice is: not to follow my advice.

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    Administrator AB's Avatar
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    Quote Originally Posted by mudnut View Post
    Can you swap it with another to see if the Tacho is ok?
    Sure if I could find one. I can't remember why but there's a reason why that happens?

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    Patrol God mudnut's Avatar
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    Quote Originally Posted by jff45 View Post
    That only covers the mechanical pump TD42. I don't know if the TD42Ti with electronic timing control and the dimples on the cam gear puts out the same signal. I've read several conversion threads where they haven't been able to get the tacho working with the Ti signal.

    It also doesn't cover the TD42T mechanical pump with EGR which reads off the IP gear

    @AB what tacho do you have working with the spacer under the sensor on the dimpled gear?
    I'm still looking for more info to post, but the signals whether ac or dc will increase with engine speed. I have seen a post elsewhere, that a bloke used a resistor to "pull up" the output signal so the original Tacho works. Also bypassing the ECU has been tried successfully.
    Last edited by mudnut; 25th November 2016 at 08:53 PM.
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    Patrol God mudnut's Avatar
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    You used a spacer, so I guess you are using a two wire sensor?

    Another bloke was having trouble too, but not a TI.

    http://www.nissanpatrol.com.au/forum...ion-type-tacho
    Last edited by mudnut; 25th November 2016 at 09:22 PM.
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