How does a tacho sensor work?

[AB]

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?

[jff45]

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.

[mudnut]

Crank angle sensor explained https://www.youtube.com/watch?v=RuIislTGOwA There is not a lot of info around for the engine revolution sender.

[mudnut]

This should shed some light on what to look for.

[jff45]

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?

[AB]

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.

[mudnut]

Can you swap it with another to see if the Tacho is ok?

[AB]

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?

[mudnut]

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.

[mudnut]

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/forums/showthread.php?11831-GQ-TD42-using-standard-ignition-type-tacho

[jff45]

The original 1990 td42 GQ one mate. It works fine but doesn't read below 900rpm.

There have been several cases of the tacho not working below 1000 rpm with the TD42 sensor wired directly to the TB45 tacho.
I bought a Dakota Digital tacho interface to solve that problem on mine. Mine works perfectly now.

[AB]

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/forums/showthread.php?11831-GQ-TD42-using-standard-ignition-type-tacho

Yep, two wire sensor.

[jff45]

This is the Dakota unit


70025
...

[AB]

Interesting it's starting to read below 900rpm a bit now but shakes until 900rpm.

For what I've been through that is ok for me now, I can live with that....lol