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Is it possible for a MOSFET to work intermittently?

Discussion in 'Troubleshooting and Repair' started by apples, Jan 20, 2018.

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  1. apples

    apples

    97
    2
    Jul 1, 2012
    I have my cars PCM computer with a faulty ignition circuit. It is a 4 cylinder engine, and there are two output pins that fire two coils for four cylinders.

    I have located two MOSFETS on the board. I suspect its a MOSFET or a smaller IC further back up the line.

    1. What is the likely hood of the fet working most of the time and then every few seconds faulting.? ( there is no bad burnt smell or any obvious signs of failure on the board)
    2. What is the chance that it may be an ic further up the line that is faulty?

    Also the MOSFET is a 52887. Can not seem to find a spec sheet on it.
     
  2. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    More chance it's a dodgy spark plug.
     
  3. Alec_t

    Alec_t

    2,904
    784
    Jul 7, 2015
    Mis-firing due to corrosion in the coil pack?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
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    Jan 21, 2010
    If the device has been in a high vibration environment (e.g. a car) then it is possible that a poor solder joint has fractured. This may produce an intermittent failure.

    The same thing could occur with bond wires inside a package, but this is much less likely.

    This is a direct answer to your question about an intermittent failure in a mosfet, it is not a statement that it is a high probability!

    Look at the board under high magnification and see if you can locate any fractured joints. Prodding the board with something insulated (e.g. a stick) may help you narrow down this type of failure which will most likely be changed by slight flexion of the board or with pressure on components (it may resolve, or get dramatically worse).
     
  5. Bluejets

    Bluejets

    4,259
    907
    Oct 5, 2014
    Get a mechanic to run a diagnostic on it.
    These things tend to get logged in the ECU for easier fault finding.
     
  6. apples

    apples

    97
    2
    Jul 1, 2012
    New coil pack, new leads, new plugs. Random "no spark" down wires 2 and 3, using a inline spark tester that lights up on each spark. You can see the no spark happen then the car stumbles.

    It's got that awful clear coat conformal coating on it which makes it hard to see any cracks. I do not have a magnification device, yes it is very hard to look for cracks with no magnification.
     
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