Tach adaptor/step up resistor | The Z Club of Great Britain
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Tach adaptor/step up resistor

Discussion in 'S30 (240Z,260Z,280Z) Electrical' started by Fairlineguy, Aug 29, 2017.

  1. Fairlineguy

    Fairlineguy Forum User

    Any one using a tach adaptor or step up resistor to get there original Rev countre to
    Work with a ecu output?
    Read numerous treads some say they have been able to get it to work others haven't
    As I would prefer not to swop out the original unit.
  2. Farmer42

    Z Club Member

    Is there no dizzy with fuel injection?

    Normally the tach works off the signal from the coil so I thought it wouldn't have made any difference if you have an ECU. There is some small modification to be made if you have swapped to an electronic ignition such as a e12-80 280ZX dizzy but again I think this is on the coil wiring.
  3. johnymd

    Z Club Member

    The zed tacho works through an inductive pickup. It senses pulses in current flow through the wire LT wire from the coil. Most of the converters I have seen just change the pulses to suit a specific Tacho. I guess anything is possible but you need to find something that doesn't send a pulse signal to the tacho as that wont work. You could measure the current changes on the factory zed tacho wire and the current change on the feed from the Toyota ecu to the ignitor pack to see if they are compatible.

    I couldn't be bothered to get mine working so bought an instrument panel from a supra and built the tacho into my zed gauge. later I replaced it with a Autometer gauge.
  4. IbanezDan51

    IbanezDan51 Forum User

  5. johnymd

    Z Club Member

    The dinoplex one looks like a good option.
  6. IbanezDan51

    IbanezDan51 Forum User

    Was cheap too - they had a board left over from a batch they built so I bought the components and they sent me that free of charge rather than me having to make a bread board version. Just soldered it up - probably cost under 10 quid. I just set it up best I could with a signal generator on a table top.

  7. Fairlineguy

    Fairlineguy Forum User

    I messaged the guys at tach match best response I received to date.
    Recon I will try this route .
    Keep you posted here is there reply to my enquiry

    Hi Neil -

    Indeed you do have a current driven tachometer. The TachMatch TM-02-I-Drive unit will operate your stock tachometer.
    My understanding is that the RB25 has a tach output signal on pin 7, which is an open-collector output. Being open-collector, it needs a pull-up resistor to get the signal operative. I would recommend a 1.3k ohm pull-up resistor for use with the TachMatch. If you wish, I could install one inside the unit for you at no extra charge. I'm not sure about the maximum sink current on the RB25 pins, I've seen on the internet that folks use 1k resistors sometimes, so I'm presuming that this slightly higher value (1.3k) should be ok, it loads the pin less than 1k. I can't find the actual spec anywhere for your ECU.
  8. IbanezDan51

    IbanezDan51 Forum User

    They were a great help to me too, I just never got round to using it. I'm sure one day it'll come in handy for something :D
  9. Fairlineguy

    Fairlineguy Forum User

    Being keen to keep the stock instruments with the rb25det .I've Just fitted the TachMatch TM-02-I tach adaptor.
    It works a treat operating my standard tach using the rb25 ecu signal output
  10. Mr.G

    Z Club Member

    Prior to going to a programmable ECU I had an original 240 tacho converted many moons ago to digital by an electronic guru in the US on HybridZ, it came calibrated too.. In the end I didn't use it as I managed to get mine working.. If you get stuck let me know and I will try to find out some more information for you. I wanted to use a digital one for more accuracy and at the time the ecu I was going to use could do a gauge swoop before you started up, which I thought would be cool...:coolgleam:
    Last edited by a moderator: Oct 8, 2017
  11. Russell

    Z Club Member

    My understanding is that they changed from the current sensing tach (240z) to a voltage sensing one (later 260z).
    I have a later version in my 260z and hoping that I can just move the feed to the ignition module on the 1JZ im fitting and it just work.

    If that is correct, couldn't you just get hold of a tach from a newer car and use that?
  12. Russell

    Z Club Member

    Actually, I just looked and I think I may be completely wrong.
    This is the tachometer from my 260z and it looks very much like a current sensing one to me?
    That screws my idea up totally.
    Was the change to a voltage sensing one a US market thing?


    Sent from my iPhone using Tapatalk
  13. Fairlineguy

    Fairlineguy Forum User

    Yep that's a current sensing tach ( inductive loop) same as in my 240z . I would guess all cars with points prior to electronic ignition will be the same.
  14. Russell

    Z Club Member

    Yet another thing to work out I need to add to my list then!

    Sent from my iPhone using Tapatalk

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