Elantra 92: the tachometer runs intermittently

Discussion in 'Hyundai Elantra / Lantra' started by Jean Castonguay, Aug 24, 2007.

  1. When the tachometer runs, it seems to display correct values.

    This leads me to hope that the tachometer is not defective but that
    the speed signal does not reach it due to an intermittent contact
    between the tachometer and the device that generates the signal.

    The tachometer is fed 12 volts from a line that also powers the
    temperature and fuel gauges; the latter work flawlessly. The
    tachometer is also grounded.

    I suspect that the third wire connecting to the tachometer is the
    culprit. I think that this wire carries a number of pulses per minute
    proportional to the engine RPM: I have not used an oscilloscope to
    look at it yet. According to the Hyundai electrical diagram, the
    signal comes from a power transistor and is filtered by a "Noise
    Filter". Most likely, this power transistor is "tickled" by the
    Engine Control Unit, the device in the know!

    Could anyone tell me where the Engine Control Unit is and what is the
    path of the signal from the Engine Control Unit to the tachometer.

    Thank you very much in advance for any help.
    Jean Castonguay, Aug 24, 2007
  2. Jean Castonguay

    hyundaitech Guest

    Your ignition coil has a tachometer interface on it. The signal goes from
    there to the noise filter you describe. The noise filter then sends the
    signal to the tachometer.

    The noise filter bolts onto the surge tank. Check the wires to the noise
    filter. Often, the insulation comes off the wires and they short

    Since the signal originates from the ignition coil, the ECM is not a
    potential cause unless your car is not running properly.
    hyundaitech, Aug 24, 2007
  3. Thank you very much, hyundaitech.

    I found the noise filter bolted on the left end of the air intake
    manifold, about 15 cm from the fuel pressure regulator. The
    resistance between pins 1 and 2 of the connector is infinity, so the
    resistor between these two pins is open.

    Could you tell me where the surge tank is located?

    Thanks again.
    Jean Castonguay, Sep 11, 2007
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