Problem with Tach - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 6 (permalink) Old 04-16-2017, 06:25 PM Thread Starter
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Problem with Tach

How do I make a 1972 240Z Tach work with a 1981 280ZX motor.
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post #2 of 6 (permalink) Old 04-16-2017, 06:49 PM
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Originally Posted by Hyrum View Post
How do I make a 1972 240Z Tach work with a 1981 280ZX motor.
I would assume it would work with no modification since I think the tach takes a signal from the coil.
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post #3 of 6 (permalink) Old 04-17-2017, 07:35 PM
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Well... The early Z's (1970-1973) take a different approach than the 1974-1978 (and later) models. The early's "sense' the current flow to the coil. The power supply to the coil from the ignition switch is looped at the back of the tach and the tach is probably sensing the amp flow.

The lates "count" the number of times the coil fires and derive an PRM value from that. They get the pulse signal that causes the coil to fire from the electronic ignition.

At any rate, they are wired completely differently. I don't know if the stock wiring is going to work once you've swapped in an EFI engine. Perhaps, if you've kept the power to the coil "pure" (wired exactly as stock and with no additional components on that wiring...) but I'm not sure. I've never had that problem since I have a 260Z. My tach however has worked with all different kinds of electronic ignition modules over the years...

edit: forgot to mention that there are tach adapters made to allow old, original tachometers to work with more modern ignition systems.

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post #4 of 6 (permalink) Old 04-18-2017, 11:32 PM
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Quote:
Originally Posted by Hyrum View Post
How do I make a 1972 240Z Tach work with a 1981 280ZX motor.
How much of the ZX motor did you swap over? Did you include the fuel injection and ECU?

Assuming the latter...

1. Study the wiring diagrams for the 72 240Z and for any year (75-78) 280Z. Focus on the ignition wiring and tachometer wiring.
2. Note the parts differences and get a 280Z tachometer and resistor.
3. Modify the wiring in the dash harness to jumper out the old tach and wire in the new tach.


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post #5 of 6 (permalink) Old 04-20-2017, 07:05 PM
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This site has gone down hill since I was last on here. The 240Z receives its tach signal from the positive current side of the ignition / coil circuit vs. later Z's. No need to screw with EFI unless it's a full turbo swap. Simply wire the ZX distributor as seen in the 240Z portion of these instructions. Its simple, quick & works as I have been running this set up on my 69 240 with the 79ZX distributor module since I bought my car - swapping over from points.
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post #6 of 6 (permalink) Old 04-21-2017, 11:57 AM
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I have a 1972 240z and have the tach wired using a pertronix coil and ignitor module. The tach Works. What if i swap it with a Mallory will it stop working?
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