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Fuse box trouble plus a misfire.

Discussion in 'Mondial' started by JLF, May 15, 2019.

  1. JLF

    JLF Formula Junior

    Sep 8, 2009
    771
    Dallas
    Full Name:
    JERRY
    #1 JLF, May 15, 2019
    Last edited: May 15, 2019
    Was looking at the fuse box just now and I saw this. It’s an air conditioning fuse. The fuse and housing had melted but the fuse hasn’t popped yet. Can anyone tell me about this? My ac works fine the last time I drove it.
    However; also my car started misfiring 3 days ago. The rpms would drop to about 600 at idle and it “feels” like it’s only firing on one bank during idle. A couple times during acceleration there was an abrupt momentary ignition cutout.

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  2. mike32

    mike32 Formula 3

    May 13, 2016
    1,897
    Uk
    Check the recommended rating of the fuse in the hand book. The fact the fuse holder is melting makes me think it has had an over size fuse fitted to keep it working. The fuse should go well before the holder does this. Is this fuse supplying the compressor clutch, and/ or the blower motor ?
    Rig up a multi meter to the cig lighter or a power source so you can see the system voltage while driving, it may be a common problem from the fuse box as they are known to fail.
    The misfire could be a lack of primary volts to the coils- measure the volts at each coil
    I have the wiring drawings if u get stuck
     
  3. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,075
    Texas
    Full Name:
    Steve Magnusson
    This is the result of a small resistance developing between the fuse's metal male tab and the female metal prongs on the PC board (not the current being too high so the fuse doesn't blow). The unwanted small resistance (like .050 Ohms) isn't high enough to affect the operation of the device(s) on the circuit, but, on a circuit that uses 10~15A, it generates a lot of heat (like dissipating 5W~10W), and the traces on the PC board tend to be much smaller than a wire so they don't conduct the heat away very well = the metal parts get quite hot and melt any nearby plastic. Can happen on any circuit that uses an ATC fuse and draws a lot of current.
     
  4. JLF

    JLF Formula Junior

    Sep 8, 2009
    771
    Dallas
    Full Name:
    JERRY
    So what should I do Steve? Pull the fuse board and clean? Replace it with a better one?
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,075
    Texas
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    Steve Magnusson
    Certainly the minimum would be to clean the contact areas of the female prongs and bend them together to restore their clamping pressure. Wouldn't hurt to have a look at their solder joints, too, as the heat can sometimes damage those or the pads/traces.
     
  6. JLF

    JLF Formula Junior

    Sep 8, 2009
    771
    Dallas
    Full Name:
    JERRY
    I assume I would have to pull the board to do that?
     
  7. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    18,075
    Texas
    Full Name:
    Steve Magnusson
    Yes. Would be a process of unplugging all the connectors (make notes!) and removing the whole assembly from the car. Then remove all the relays and fuses (make notes!), and you'll see the screws on the backside holding the PC board to the plastic shell. With the plastic shell removed, the female terminals on the PC board will be accessible.
     
  8. JLF

    JLF Formula Junior

    Sep 8, 2009
    771
    Dallas
    Full Name:
    JERRY
    Thank you
     
  9. AndruL

    AndruL Karting

    Apr 4, 2018
    111
    Full Name:
    AndruL
    Also beef up the offending traces on the PCB by paralleling them with 12AWG wires...
     
  10. Subito Grigio

    Subito Grigio Karting

    Jun 2, 2009
    154
    ... and it may be prudent to search FChat Mondial and 308 chat files for the many descriptions about fuse box, printed circuit, melted stuff, etc., before you open up that fuse box. Such a review will help you better understand most of the possible failure aspects. Strongly recommend doing the homework. Might save you time and money!




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