240z (280z block) - rev counter not working - troubleshooting tips? | The Z Club of Great Britain
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240z (280z block) - rev counter not working - troubleshooting tips?

Discussion in 'General' started by Graeme - CZ, Apr 28, 2019.

  1. Graeme - CZ

    Graeme - CZ
    Z Club Member

    Hi all,

    The rev counter on my 240z has never worked. Before I start trying to diagnose this, I am sure someone can probably advise me. Car has a 280z 5 speed block in it. My first question is that has the engine change rendered the rev counter unworkable in it's current state? I don't know whether it is mechanical or electronic?

    Is there an easy fix or things to check out?

    Regards, Graeme
  2. dav118118

    Z Club Member

    Take the dizzy cap off and u can see whether there are points or not. As it’s a later engine it will most likely have an electronic dizzy with no points. There are other threads on here on how to reconnect the wiring to get your tach working, that’s if you still have all the original wiring in place, which I didn’t
    jonbills likes this.
  3. Graeme - CZ

    Graeme - CZ
    Z Club Member

    Yeah, it's an electronic distributor I have. No idea about wiring though. Any tips on threads worth checking out?
  4. Farmer42

    Z Club Member

    Have a look at this site which is where I got the wiring diagram from.


    If you have the electronic dizzy with a black module with 2 terminals, this should do it. There are 2 wires that need joining together to get the tach working. This can be done near the coil or at the ignition switch end. You no longer need the ballast resistor but you do need to swap your coil to a 1.5 Ohm coil otherwise it will not run very well and your coil may overheat & fail - been there & done it!!
  5. Graeme - CZ

    Graeme - CZ
    Z Club Member

    Thank you Farmer42
  6. adrianf240z

    adrianf240z Active Forum User

    In a lot of cases with the rev counter not working and the dizzy and coil has been changed and the ballast resistor has been removed people tend to take the power lead to the ballast and put it directly to the + side of the coil. Doing this stops current going to the rev counter. the outlet side of the ballast the wire goes all the way through the loom and on to the rear of the rev counter where it forms a small loop through a plastic block then goes all the way out to the + side of the coil. When the coil fires it creates a pulse that goes through the coil + wire so the rev counter counts these pulses, so if your wiring has left out the ballast cable you may have a spare wire by your coil. All you need to do is take the coil + wire and connect it to the loose cable so the rev counter is back in the loop and the rev counter should work.
    jonbills likes this.
  7. Seikoking

    Z Club Member

    51BB506E-A486-44E0-B5C6-E5E315DAA0A2.jpeg Apologies for the thread hijack but I’ve had the same issue with my L28. Based on the comments above, Adrian, would you suggest I connect the cut short spare wire (green in the centre of the picture above the right hand side ht lead) in the pic to the positive connection on the coil?

    What is the best best way to check it first?
    Can I do any damage?

    Sorry for the stupid questions, I’m still learning sharply since entering Z ownership!
  8. Fairlineguy

    Z Club Member

    As Adrian240z said the 12v feed to the coil goes via the tach ( inductive loop)
    There should be two black and white wires near the coil this is the wire that loops the tac
    Also a green and white wire 12v feed I expect this has been connected direct to the coil?
    Take it off the coil and connect to one of the black and white wires the other black and white then goes to the coil
    jonbills likes this.

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