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Thread: Aftermaket Tacho

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    Aftermaket Tacho

    Hi,
    I've bought an aftermarket tacho and am having difficulty connecting it up. It says you can wire it up off of the coil/distributor or the power transistor. I've attempted to wire it up off of the power transistor, but it reads incredibly low, around a quarter of what i would expect it to. It has 4,6 and 8 cylinder modes and is set on 4. I have wired it up on the side f the power transistor that has 4 cables {4 red/colour} rather than the side tat has 5 cables {4 red/colour and a black}.

    Any help on this would be appreciated.

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    It might not be as low as a quarter but, its definitely between that and half.

    I connected it up to the tacho output from the ecu today, but that didnt even make the gauge move, so i guess it's not compatible witht he standard s13 ca18det tacho signal?

    This is quite frustrating.

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    Try it on the main ground to all the coil pack loom as that should read all 4 cylinders firing where as you may only be reading the signal from 1 coil

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    Thanks for the suggestion. I went and tried this today, but to no avail, so i tried on the ground of the power transistor, working under the same theory, but no joy.

    I aslo tried putting a 10k resistor between the ecu tacho signal and +12v on the back of the tacho, as i had read it suggested a couple of times on drifworks, but again got nothing. If i hadn't got it reading low before i would be inclined to say the tacho doesn't work at all, but i know that not to be the case.

    Has no one here done an engine conversion with a ca18det? How did you get a working Tacho if not using original clocks?

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    i have an aftermarket tacho. i teed it off the line to the back of the original clocks.

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    Unfortunately the engine is no longer in an S-body so there are no original clocks in there to take a feed off of. I guess that's why i'm having so much trouble.

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    yeah the signal is a square wave from the ecu, you need a resistor in line but needs to be the same as the one in the original tacho or you will fry that section of the board in the ecu.

    you can gut an original tacho and only use the board to fit it in line with the new tacho

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    There isn't a 4 cylinder ignition output. The CA18DET has individual coil on plug ignition and is a single cylinder ignition.

    4/6/8 setting are for distributor systems that have a single HT system that fires for every cylinder.

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    So... it's impossible to have an aftermarket tacho work on a ca18det if it no longer has the original s13 dials? I know there are some guys who have put the engine into kit cars and older vehicles, there must be a workaround, but i'm unable to find it through searches.

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    https://www.autometer.com/resources/...faq_view/id/44
    http://www.marshallinstruments.com/t...er_adapter.cfm
    https://www.msdperformance.com/produ...ers/parts/8913
    http://www.autometer.com/tach-adapter.html
    https://www.the12volt.com/installbay...asp?tid=140717

    If you are any good with electronics what you need is a Voltage Controlled Oscillator (VCO), connected to tach output, calibrated to produce 2 12v pulses for each rev.

    Or splice into the CAS 180° signal, use a high impedance (no load) input device (FET), and a Darlington pair output. CAS 180° is the required 2 pulses for each rev but they are only about 2°. Tach input may be needing much longer dwell which means a pulse stretcher is also needed (want about square wave).

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    Guest jj205mi16's Avatar
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    skyshack is much more clued up with this than me, but what i did was take the original tacho, pull the face and the needle off of it, there isnt much left just a small board. wire it in along with your new tacho, and it will give the signal wire the output you need.

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    Thanks guys, that's given me some homebrew things to try, if they don't work i will have to order the autometer adapter in from America.

    I will avoid skyshacks ideas as they are way above my level of skill and understanding in electronics.

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    A divide by 90 on the CAS 1° signal. There are 180 slits in the timing disc, each is 1° wide.

    So that's a divide by 10 cascaded into a divide by 9.
    http://www.electronics-tutorials.ws/...r-circuit.html
    http://tradeofic.com/Circuit/5097-DI..._REGISTER.html

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