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Thread: How To ... Tacho Booster

  1. #1
    Junior Member Automotive Encyclopaedia infotechplus's Avatar
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    Default How To ... Tacho Booster

    Background

    There have been a number of questions and threads devoted to the problem some Toyota models have with outputting revs to an aftermarket tacho. My Hilux conversion had a similar problem on two different tachos including the Speco Thomas unit.

    The diagram most widely circulated is the one in the following thread:

    http://www.toymods.net/forums/showthread.php?t=3710

    Using that diagram I have enlisted the aid of a friend (and electronics guru) Paul to assist in modifying a relay to work as a tacho booster.

    I started off with a VW/Audi relay that I got along with a few others from a wrecked Audi.



    This was a convenient starting point but you could use any relay as long as you can 'crack' it open to get at it's insides. This is to keep the whole thing nice and neat, and when it's finished re-installed in it's plastic case.

    Here's the four points we used. The fifth pin was removed to avoid any confusion over where the connections go.



    We assigned the following pins:

    Pin 30 became GND (Ground)
    Pin 87 carries the signal from the Igniter IGN, the black wire that sends RPM from the ECU
    Pin 86 became the output signal going to the tacho
    Pin 86a (small width pin) is the PWR or 12v +ve. We hardwired this pin with a length of wire that connects to the power source via bullet connection.
    Pin 85 was removed.

    Note: we have reassigned the pins from what they would normally be for simplicity and make it easy to put the new components on the small board. You could do the same and use different pins. This worked for us.

    So the amended diagram looks like this:



    Modifying the relay

    This is the unmodified relay with the plastic case removed.



    Here's another view:



    First we removed the items we didn't need, The board was turned over and desoldered, and the contacts removed from the coil. Only the coil itself was left untouched. That's all you need from any relay.

    We had to drill two small holes in the underside of the board to accommodate the amended wiring as outlined in the original diagram. These are shown in the next photo.



    The diode is linked to one end of the coil, then the other end to the resistor, which is joined to the transistor. The transistor is then linked to the other end of the coil with short piece of shielded wire.

    We also joined two contact points to bridge them.

    Basically the flow from the IGN to the tacho is linear. So firstly we put the diode on the board. Here it is:



    Then the diode was connected to the resistor but we put the transistor in next so all three were joined.



    Here's the resistor:



    The tacho booster was checked on the test bench and a 5V square wave gave a 12v output so everything was working correctly. I haven't tested the unit in the 'real world' yet but I'll do that as soon as I can (probably tomorrow afternoon).

    I couldn't find a data sheet on a BC433 but I did for BD681, BC345 (which we used) and the BC432.

    Here they are:

    BC345 Datasheet
    BD681 Datasheet
    BC432 Datasheet

    Cheers,

    Peter
    Last edited by infotechplus; 24-09-2017 at 11:05 PM. Reason: Added links to spec sheets
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  2. #2
    JZ Powered Too Much Toyota EldarO's Avatar
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    Default Re: How To ... Tacho Booster

    awesome write up, try using the MACRO mode on your camera if ya havent this time, it'll give you clearer shots.

    Well done, ill be keen on seeing your results

    Elmo.

  3. #3
    Junior Member Automotive Encyclopaedia infotechplus's Avatar
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    Default Re: How To ... Tacho Booster

    Quote Originally Posted by EldarO
    awesome write up, try using the MACRO mode on your camera if ya havent this time, it'll give you clearer shots.

    Well done, ill be keen on seeing your results

    Elmo.
    Elmo, I took some shots 3 or 4 times without success. I'll have to see if I've got a Macro option on my little Canon PowerShot DC and try your advice. I'll have a definitive result tomorrow but I know Paul does very good work so have every faith in this working (even if he is a VW man).

    Cheers,

    Peter
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  4. #4
    Junior Member Automotive Encyclopaedia 2jzhilux's Avatar
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    Default Re: How To ... Tacho Booster

    let us know if this works in the car if so that would be awesome

  5. #5
    JZ Powered Too Much Toyota EldarO's Avatar
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    Default Re: How To ... Tacho Booster

    i didnt mean to discredit the work or anything mate! i just meant im hanging out to see if it'll work, some things dont go as planned in practise.

    apologies if it was taken the wrong way

    the MACRO option is usually a picture of a single flower on the setting button on the camera.

    Elmo.

  6. #6
    Junior Member Automotive Encyclopaedia infotechplus's Avatar
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    Default Re: How To ... Tacho Booster

    Quote Originally Posted by EldarO
    i didnt mean to discredit the work or anything mate! i just meant im hanging out to see if it'll work, some things dont go as planned in practise.

    apologies if it was taken the wrong way

    the MACRO option is usually a picture of a single flower on the setting button on the camera.

    Elmo.

    Definitely not taken the wrong way.

    I accepted your comment as genuine advice. Sorry if my reply suggested otherwise.

    Cheers,

    Peter
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  7. #7
    Junior Member Automotive Encyclopaedia infotechplus's Avatar
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    Default Re: How To ... Tacho Booster

    Quote Originally Posted by ecotechilux
    let us know if this works in the car if so that would be awesome
    Tonight I connected up the Tacho Booster to my AutoGauge Monster Tacho, and then made the connections to the Lux using Pin 2 (the black wire from the igniter) on Plug G1.

    I had to reconnect the orange wire on the tacho as I had been using it in the race car (4 cyl) last year so that it was 6 cylinder compatible.

    The tacho worked.

    However, I then connected the tacho directly to the igniter wire (leaving everything else as is) and it still worked so I can't give a definitive answer as to whether the Tacho Booster actually boosts the signal. It does work, or more to the point, it doesn't stop the signal from reaching the tacho.

    The only way to test it further is to buy another Speco Thomas unit as I returned mine last week. Or if someone has a non-functioning tacho and wants to test my Booster let me know and I'll mail it to you (and you can send it back after testing it).

    Cheers,

    Peter
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  8. #8
    Junior Member Automotive Encyclopaedia
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    Default Re: How To ... Tacho Booster

    I built one and tryed it on my 7MGT but it didnt work , im guessing the 7M has a diff output to the JZ engines.
    Dave

  9. #9
    Junior Member Automotive Encyclopaedia infotechplus's Avatar
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    Default Re: How To ... Tacho Booster

    Quote Originally Posted by cambelt1
    I built one and tryed it on my 7MGT but it didnt work , im guessing the 7M has a diff output to the JZ engines.
    Dave
    What setup do you have cambelt1?

    Factory tacho or aftermarket? Which brand/model?

    Where are you obtaining the RPM signal from? ECU? Igniter? Check connector IGN?

    Cheers,

    Peter
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  10. #10
    Current UZA80 owner Chief Engine Builder JustCallMeOrlando's Avatar
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    Default Re: How To ... Tacho Booster

    I've got one on my car with a 1GGTE. If you get a more common relay, you'll find it probably has more room inside!
    Teh UZA80 - Project Century - Remotely p00'd by association

  11. #11
    Raastler Grease Monkey
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    Default Re: How To ... Tacho Booster

    Someone make me one

  12. #12
    Founding ****** Automotive Encyclopaedia Mos's Avatar
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    Default Re: How To ... Tacho Booster

    Most older tachos need a much higher voltage, in the order of 40V or so. The factory igniter on an MX83 7M-GE produces around 40V - the tacho will work with lower voltages, but I haven't tested it to see how low it will go - worked fine with 36. A transformer or relay coil should spike a lot higher - I clamp the output of mine to around 40V.

    When you say 5V in , 12V out, did you scope the signal on the output?
    Your circuit should produce a much higher voltage - if you're only getting 12V out something isn't working properly. The coil seems to be acting as a pullup resistor only, and that's why you'd be getting the 12V only.

    Mos.
    Admin, I.T., Founding Member, Toymods Car Club Inc.
    2000 IS200 Sports Luxury 1UZ-FE VVTi, 1991 MX83 Grande 2JZ-GTE (sold)

  13. #13
    Junior Member Automotive Encyclopaedia infotechplus's Avatar
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    Default Re: How To ... Tacho Booster

    Quote Originally Posted by Mos
    When you say 5V in , 12V out, did you scope the signal on the output?
    Yeah we output the signal to a scope. My buddy is not in today so I can't verify the output voltage but I'll ask him next Monday.

    Cheers,

    Peter
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  14. #14
    JZ Powered Too Much Toyota EldarO's Avatar
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    Default Re: How To ... Tacho Booster

    Quote Originally Posted by cambelt1
    I built one and tryed it on my 7MGT but it didnt work , im guessing the 7M has a diff output to the JZ engines.
    Dave
    7MGTE and 1JZ/2JZ are the same.

    7MGE is different.

    so using a 7MGE dash with a GTE/JZ is not gonna work without a converter.

    Elmo.

  15. #15
    Gary Motorsport Inc. Too Much Toyota takai's Avatar
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    Default Re: How To ... Tacho Booster



    One i made up tonight
    -Chris | Garage takai - Breaking cars since 1998
    Sparky - AE86 IPRA Racer | RZN149 Hilux - Parts and Car Hauler
    I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself. - D.H.Lawrence

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