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Lamborghini Diablo Engine Management question

Discussion in 'Technical Q&A' started by Sledge4.2, Sep 2, 2016.

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  1. Sledge4.2

    Sledge4.2 F1 Rookie

    Oct 19, 2007
    4,784
    Marin
    Full Name:
    Geno
    #1 Sledge4.2, Sep 2, 2016
    91 Diablo (pre-OBDII)

    There are two LIE computers, one for each bank with 35 pin connectors to each LIE. There are diagnostic procedures outlined in the WSM, testing ohms and voltages from various LIE harness terminals to test functionality of the connected systems.

    I am failing two tests:

    1. “Engine speed and TDC and Phase sensors shield connection”, measurement be ~0.2ohm, I have an open circuit.

    2. "Lambda probe shield”, measurement should be ~0.2ohm, I have an open circuit.

    Looking at the wiring diagram, the engine speed and TDC sensor, lambda probe, and phase sensor all share the same shield connection (inside the wiring harness).

    The phase sensor and engine speed and TDC sensor resistance tests pass within acceptable ohm.

    There is a crude on board diagnostic via blinking dash light, and I am NOT tripping any codes (including not tripping “lambda probe inactive”, “lambda probe signal constantly inactive”, or “lambda probe signal constantly rich”. “phase sensor on camshaft” or “engine speed and TDC sensor”.

    I am however tripping codes for battery voltage and coolant temperature sensor (both sensors new).

    What started me down this path was a rich running condition when warm, which I thought to be the water temperature sensors, and when I replaced them, the codes went away but popped back on under hard throttle.

    Then I did the diagnostic procedures found the two shield errors above.

    Could the lambda sensor(s) be bad, and still not throwing a code? A wiring problem with continuity of the connected systems to the common shield?

    Any thoughts from the fchat community appreciated,
    Geno
     
  2. cizeta

    cizeta Rookie

    Jul 2, 2010
    7
    great white north
    Full Name:
    Craig Zuidema
    #2 cizeta, Sep 5, 2016
    My first question would be, did this occur after a service? If so, revisit all those items. The OBD1 diagnostics of Lambo and everyone else of that era leave much to be desired, so you will have to use test equipment to diag this issue. I think you'll need something more sophisticated than a DVOM to test, preferably an oscilloscope, where you can verify the waveform of the ckp and cmp sensors, koer. These are simple analog sensors, not digital, so if you can backprobe the sensor connection either at the component or ecu to take your readings, the signal waveform can be analyzed to determine whether it is a component, ecu or mechanical fault. Check all your engine grounds first. I'm unaware what your financial situation is, but Picoscope is my favorite, something that I would recommend to any pro diagnostic tech, an advanced tool that can be used on any car. If the sensors conform to established specs, you'll have to verify your wiring from component to ecu, ecu grounds, and even the battery connections, since they aren't the easiest to get to on this car. It has been a few years since I serviced these cars, and my experience with LIE is limited to 2 Diablos and a LM. I'm not sure if the ecu's are swappable as on BMW, Ferrari and MB, but it might be a test of last resort. HTH, Craig
     

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