How to get your Tach to work with modern ECU signals

johnymd

Club Member
Russell kindly built one of these for me a while ago and I gave him the wrong info for my v8. I said it worked on 8 pulses but actually its only 4 so it read half the revs. I finally got around to calibrating it against my ECU reading and by adjusting the pot I could get it correctly reading throughout the range. I didn't change any resistors.
 

Russell

Club Member
Russell kindly built one of these for me a while ago and I gave him the wrong info for my v8. I said it worked on 8 pulses but actually its only 4 so it read half the revs. I finally got around to calibrating it against my ECU reading and by adjusting the pot I could get it correctly reading throughout the range. I didn't change any resistors.

Glad that worked out for you. Would have happily rebuilt it for you if it hadn’t had worked.


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datsunnyit

Well-Known Forum User
Only just seen this.

That looks like it will just work as it is the newer version that doesn’t use a coil based pickup.


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Hi Im interest for now, only make a work test for my RPM removed from car. What type of signal voltage connect at the wires to test the rpm ? use battery 1.5volt ? how tesat to check if work or not. thank you
 

Russell

Club Member
Hi Im interest for now, only make a work test for my RPM removed from car. What type of signal voltage connect at the wires to test the rpm ? use battery 1.5volt ? how tesat to check if work or not. thank you

So you have your tacho out of the car and you want to test it on the bench?

You would need a signal generator to simulate the car and not knowing exactly what you have and having no direct experience I would be guessing.

What you can see on my thread above is a PWM signal generator. Very cheap from ebay and will produce a signal with an amplitude matching its input voltage as well as being able to adjust the frequency and duty cycle to match your application.
Something like this -
https://www.ebay.co.uk/itm/Adjustab...m570.l1313.TR1.TRC0.A0.H0.Xpwm+generator.TRS0
 

Russell

Club Member
I still have a load of these boards left over if anyone needs their tach repairing or upgrading.

I have my original one that’s converted already and would like to swap it for a broken one that I can cut up guilt free.


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tyroguru

Club Member
This looks great! Do you know if Jon managed to get a tach that went to 10k? Even better, a Spinal Tap Tach that went to 11k for when you need that "extra push over the cliff" :) .
 

Russell

Club Member
This looks great! Do you know if Jon managed to get a tach that went to 10k? Even better, a Spinal Tap Tach that went to 11k for when you need that "extra push over the cliff" :) .

If someone has a 10k face its just a case of calibrating it.

Could just print a 10k face out and glue it on!

As long as the numbers are equally spaced and start and end at the factory locations, you could go as high as you want!
 

jonbills

Membership Secretary
Site Administrator
I got a 10k tach from Speed Hut in the end. Very nice, but pretty pricey.

index.php

https://zclub.net/community/index.php?threads/speeduino-installation.23302/page-4#post-296034

I did nearly get there with a cheap ebay one like this: https://www.ebay.co.uk/itm/2-52mm-0...051793?hash=item1f0e4f1c51:g:CbIAAOSwj0NekNbC
It worked pretty well, but I failed to sort out getting a Z size 10k face printed so got frustrated and went with Speed Hut.
 
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Russell

Club Member
Just the quality of the printout that would be an issue for me. Maybe design in photo shop and get it professionally printed on Satin vinyl. Would look incredibly close to standard.
Then simply adjust the calibration on the tach.


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skinjim

Club Member
I still have a load of these boards left over if anyone needs their tach repairing or upgrading.

I have my original one that’s converted already and would like to swap it for a broken one that I can cut up guilt free.


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Hi Russell, my tach hasn't worked since it was converted from points to dizzy, forgive my ignorance but will this fix my issue, or is it just for ECU conversions?

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peter_s

Club Member
I wired it back into the original input posts.
For the signal wire, I took the induction loop or whatever it’s called out and wired it straight into the post.

1a7761e50a555377f405f19c23998cb5.jpg
Hi Russel,

I'm about to start installing the PCB in my tacho. This step is a little unclear for me: Did you remove that induction coil from the circuit and threw it in the bin?
 

johnymd

Club Member
As this tacho thread has some good information I though I'd tag my question onto it. I have an early 260z with the current loop type tacho and a 280zx dizzy. The car is also totally rewired. The coil/tacho circuit is simple and just goes from coil fuse through tacho loop and to the + terminal of both dizzy and coil. Trouble it I cant get the tacho to work and I have no spares to test with. I do have several non current loop type with just the single input. So. my question is can I just take a wire from the - coil terminal to the tacho input. I have seen people mention it needs a 2.2kOhm resistor in series. Can anyone confirm this?
 

peter_s

Club Member
As this tacho thread has some good information I though I'd tag my question onto it. I have an early 260z with the current loop type tacho and a 280zx dizzy. The car is also totally rewired. The coil/tacho circuit is simple and just goes from coil fuse through tacho loop and to the + terminal of both dizzy and coil. Trouble it I cant get the tacho to work and I have no spares to test with. I do have several non current loop type with just the single input. So. my question is can I just take a wire from the - coil terminal to the tacho input. I have seen people mention it needs a 2.2kOhm resistor in series. Can anyone confirm this?
If you pull the signal from the coil you need a heavy duty drop down resistor. I don't know the voltage from the coil, but probably a 4W or 5W resistor. Otherwise you'll fry the circuit in your tacho!
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
As this tacho thread has some good information I though I'd tag my question onto it. I have an early 260z with the current loop type tacho and a 280zx dizzy. The car is also totally rewired. The coil/tacho circuit is simple and just goes from coil fuse through tacho loop and to the + terminal of both dizzy and coil. Trouble it I cant get the tacho to work and I have no spares to test with. I do have several non current loop type with just the single input. So. my question is can I just take a wire from the - coil terminal to the tacho input. I have seen people mention it needs a 2.2kOhm resistor in series. Can anyone confirm this?
John, that's my setup on both my 240 and early 260. No problem.
 
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jonbills

Membership Secretary
Site Administrator
As this tacho thread has some good information I though I'd tag my question onto it. I have an early 260z with the current loop type tacho and a 280zx dizzy. The car is also totally rewired. The coil/tacho circuit is simple and just goes from coil fuse through tacho loop and to the + terminal of both dizzy and coil. Trouble it I cant get the tacho to work and I have no spares to test with. I do have several non current loop type with just the single input. So. my question is can I just take a wire from the - coil terminal to the tacho input. I have seen people mention it needs a 2.2kOhm resistor in series. Can anyone confirm this?
I've got a working spare @johnymd, I could post it down to you and pick it up later when I collect the lift.
 
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