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Thread: Speed cut woes.

  1. #1
    Junior Member Backyard Mechanic
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    Default Speed cut woes.

    I have done an Aristo conversion on my R31 skyline and I don't even have the main speed sensor hooked up. But the ECU must still be figuring out speed from the other speed sensor and cutting the show at 180. From what I hear, normally the main speed sensor signal goes to the Speedo head then the signal gets modified and comes back to the ECU. This is the signal I don't even have connected at all. (everything works 100% fine though). Now how do these speed cut defenders work? I hear they grab this signal from the Speedo head, divide it then send it back to the ECU? Is this right? Wouldn't this stuff around with auto shift points though?

  2. #2
    Toymods V8 Member Too Much Toyota CrUZida's Avatar
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    Default Re: Speed cut woes.

    All they do is plateau the speed into to the ecu at about 170kph.
    So the ecu thinks you are only doing 170, even thought you are doing much more.

    Yes, it does play havoc with the Drive-O/D shift (ie, it won't do it while your foot is flat), but if you back off it will change into O/D and then put the boot back into it.
    Peewee
    1985 MZ12 Soarer - 1UZ Powered
    2013 86 GTS

  3. #3
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    Default Re: Speed cut woes.

    Cool so the frequency is kept as normal up untill 170, then the frequency just stays at that point? And I guess it does not shift into 4th becuase 3rd revs out over 170 which therfore makes the ECU think its not time to go into 4th gear yet? Are sure it does not just divide the signal by a ratio the whole time?

  4. #4
    Toymods V8 Member Too Much Toyota CrUZida's Avatar
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    Default Re: Speed cut woes.

    3rd revs out to about 200 with a 3.909 diff, 180 with a 4.1, 210 with a 3.727 (etc)

    I can't speak for ALL speed cut units, but that is how most work.
    Peewee
    1985 MZ12 Soarer - 1UZ Powered
    2013 86 GTS

  5. #5
    Junior Member Backyard Mechanic
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    Default Re: Speed cut woes.

    Cool, so the non shifting into 4th prob is not going to bother me on the quarter mile unless I can run 124mph. Thats all I was worried about. I think I will hit 180 though

    Do you have to buy a certain type for the car or are these things adjustable?

  6. #6
    Toymods V8 Member Too Much Toyota CrUZida's Avatar
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    Default Re: Speed cut woes.

    AFAIK they are a generic unit.

    Whether its a generic 'toyota' unit, as opposed to a generic 'nissan' unit I dont know.

    But one designed for a Soarer/Supra/etc should work on yours.
    Peewee
    1985 MZ12 Soarer - 1UZ Powered
    2013 86 GTS

  7. #7
    I definitely ain't a Chief Engine Builder wagonist's Avatar
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    Default Re: Speed cut woes.

    I'm waiting for a 2nd hand generic fueltronics one to arrive in the post.
    It only has 4 wires. Ign on, earth, SS in, SS out, & a laptop port.
    Cut the SS wire & put the box in the middle & wire the rest up.
    Go for a drive at a preset speed to program the box via the laptop. Give the speed at which you want the intercept to occur at.
    Done.

    Not sure about other units though.

  8. #8
    Junior Member Backyard Mechanic
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    Default Re: Speed cut woes.

    That sounds pretty cool. How much did that cost?

  9. #9
    I definitely ain't a Chief Engine Builder wagonist's Avatar
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    Default Re: Speed cut woes.

    It was $120 from another forum.
    They run at around $300ish new I think (I haven't needed one for 4 years because the Caldina isn't fitted with one)
    I think there may be cheaper one's around, though.

    Importers may have some half-cuts fitted with them.

  10. #10
    Founding ****** Automotive Encyclopaedia Mos's Avatar
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    Default Re: Speed cut woes.

    The aristo auto gearbox has a bipolar speed sensor (SP2) for the shift points on the extension housing. If you don't have the main speed sensor hooked up (SPD or SP1 pin) then the ECU must be speed cutting off the SP2 signal.

    AFAIK all the speed cut defenders intercept the SPD signal (squarewave). The SP2 signal is generated by an inductive pickup and to my knowledge there isn't anything that intercepts that (but I could be wrong).

    You could disconnect the SP2 signal, reinstate the SPD signal, and install the speed cut defender on the SPD signal. (The auto will shift off the SPD signal if the SP2 signal is not available).

    Thoughts?

    Mos.
    Last edited by Mos; 06-07-2006 at 11:31 PM.
    Admin, I.T., Founding Member, Toymods Car Club Inc.
    2000 IS200 Sports Luxury 1UZ-FE VVTi, 1991 MX83 Grande 2JZ-GTE (sold)

  11. #11
    Toymods V8 Member Too Much Toyota CrUZida's Avatar
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    Default Re: Speed cut woes.

    Sounds feasible.
    Peewee
    1985 MZ12 Soarer - 1UZ Powered
    2013 86 GTS

  12. #12
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    Default Re: Speed cut woes.

    What does the wave form look like from the SP2 2 wire sensor? Isn't it a square wave? If it is I thought I would be able to configure the speed cut device in the same way as normal. I was a bit worried about it though.

    The reason I dont have the 3 wire sensor hooked up is becuase the engine is in a skyline and it does not have the signal divider circuit on the speedo head that is needed to correct the signal before it can be hooked back up to the the ECU. ATM the 3 wire sensor just runs my speedo with 2 jaycar speedo correctors. It was a real PITA to get the speedo to work with it as it is. To hook it up, I would need to get the signal divider circuit right, then intercept it with the speed cut defender. I was seriously hopeing to avoid this.

    If this the device can't work with the 2 wire sensor I had another idea. Using a jaycar frequency switch to just turn the 2 wire sensors output off totally before the frequency reaches whatever it is at before 180km/h. Not sure what effect this would have though. With anyluck it will stay in 3rd gear and not try and go back to first or second

  13. #13
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    Default Re: Speed cut woes.

    I've got my Fueltronics unit now, but I know where there's another one.
    It doesn't do anything with the wave until the interrupt point.
    It wouldn't matter whether you hooked this particular unit up before or after your divider circuit because it is laptop programmable.

  14. #14
    Junior Member Backyard Mechanic
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    Default Re: Speed cut woes.

    I dont have a divider circuit though. My ECU runs of the 2 wire sensor only and this might be a sine wave not a square wave.

  15. #15
    Founding ****** Automotive Encyclopaedia Mos's Avatar
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    Default Re: Speed cut woes.

    Quote Originally Posted by 2JZR31
    What does the wave form look like from the SP2 2 wire sensor? Isn't it a square wave? If it is I thought I would be able to configure the speed cut device in the same way as normal. I was a bit worried about it though.
    It's a waveform typical of an inductive sensor - I'll try to describe it.
    When the rotor approches the pickup, the voltage rises up to a peak, then as the edge of the rotor passes by the pickup the voltage sharply drops, crosses zero and goes negative to the same peak as the positive. Then as the rotor moves away from the pickup the voltage returns to zero. The waveform is diagonally symetric.

    Try this:
    http://www.picotech.com/auto/wavefor...e_running.html

    Quote Originally Posted by 2JZR31
    The reason I dont have the 3 wire sensor hooked up is becuase the engine is in a skyline and it does not have the signal divider circuit on the speedo head that is needed to correct the signal before it can be hooked back up to the the ECU. ATM the 3 wire sensor just runs my speedo with 2 jaycar speedo correctors. It was a real PITA to get the speedo to work with it as it is. To hook it up, I would need to get the signal divider circuit right, then intercept it with the speed cut defender. I was seriously hopeing to avoid this.
    You don't need the divider. The speed sensor on the aristo spits out 4 pulses per revolution of speedo output, which is the same as what the ECU needs, so you can hook it up directly to the SPD input.
    Older engines, such as 1G-GTEs etc out of G/MZ20 soarers used a speed sensor that generated a 20 pulse per rev of speedo output, needing a division by 5 to generate the 4 ppr needed by the ECU.

    Quote Originally Posted by 2JZR31
    If this the device can't work with the 2 wire sensor I had another idea. Using a jaycar frequency switch to just turn the 2 wire sensors output off totally before the frequency reaches whatever it is at before 180km/h. Not sure what effect this would have though. With anyluck it will stay in 3rd gear and not try and go back to first or second
    Yeah, I had a similar idea (to disconnect all available speed signals) - for about a microsecond
    Taking into account that it won't change out of first if it has no speed signal present, it can be expected that it will try to change back to first...
    Not something I would like to try

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

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