1uz VVTI swap starts but e-throttle doesn't work

Discussion in 'Diagnostic & Repair Tech' started by 1uzCelica, May 10, 2018.

  1. 1uzCelica

    1uzCelica New Member

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    Hi all,

    Friends and I have a VVTI 1UZ from a 1998 LS400 swapped into a Mk2 Celica. We went through the wiring and paired off what we didn't need, hooked up what we think we did and are able to start the engine ok, its able to idle happily. Trouble is the e-throttle doesn't respond to the Accel position sensor movement. What we have:

    1) Junk yard vvti 1uz from LS400
    2) Random LS400 ECU off ebay that came with a key so we could defeat the immobilizer
    3) external FPR to utilize the stock Celica fuel return line
    4) all emissions stuff removed
    5) manual conversion, no automatic trans involved

    What we've tried:

    1) swapped an entire different throttle body assembly with new stepper/throttle motor, Accel position sensor and Throttle position sensor from a junk yard GS400 - same symptom, no ethrottle movement
    2) put an oscilloscope on the coil output pairs to the stepper motor, don't see any signal on it.
    3) engine is able to rev once we hit the last 10% or so of throttle position where it manually engages the butterfly (limp mode)
    4) Can see TPS moving ok w/ an OBDII reader

    questions:

    1) We are trying to separate if this is limp mode i.e. is the ECU refusing to move the throttle because it thinks something else is wrong or if the ECU output or the stepper itself is bad.
    2) Does anyone know if the throttle motor should operate when the engine is not running but the ignition is on? Would be nice to test this w/o having to asphyxiate ourselves w/ exhaust :)
    3) Anyone know of a specific signal that if missed/not hooked up would cause the e-throttle not to respond? Or is that the ECUs reaction to a host of potential problems? Wondering if there is anything related to the auto trans or shift selector that would cause this?
    4) can we change the throttle actuation to a purely cable driven setup without the ECU freaking out about lack of APPS and TPS sensors in turn being accurate and still forcing some sort of limp mode (if we can't figure out the e-throttle, brute force...)?
    5) is there a calibration procedure for the e-throttle? Saw somewhere a recommendation to turn on the ignition, hold the pedal to the floor for 30 seconds and then turn it back off. No idea if this is fact or fiction.

    Any/all tips appreciated!
     
    Last edited: May 10, 2018
  2. Zuffen

    Zuffen Super Moderator Staff Member

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    I've had similar problems with an LS3 in one of my cars.

    The problem ended up being a voltage discrepancy between the pedal and the throttle body.

    For safety as you accelerate the throttle pedal sends 2 signals to the TB. One signal rises in voltage whilst the other falls. if they go out of balance it throws a code and no pedal.

    I'd check the wiring between the pedal and TB to see if you have a high resistance joint or wire.

    I know on my LS3 the TB cycles each time you turn the ignition on. This is something to do with ensuring the voltages balance before it starts.

    I'll be honest I would have left the pollution gear in place until I knew it ran right. A whole lot less potential problems to sort.
     
  3. George_R

    George_R Member

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    What you did NOT do:
    1 Plug a scan tool and see particular trouble codes, instead of guessing and poking fingers into different holes
    2 a/t emulation device will be needed
     
  4. gloverman

    gloverman Well-Known Member

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    Is there power to +bm? I see it missed lots.
     

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