Simultaneous misfire on a pair of cylinders? N/A 2.5L

Discussion in 'General Motoring' started by David, Jul 30, 2004.

  1. David

    David Guest

    My 2003 Forester XS, 15k miles, just issued an apparent simultaneous P0301 & P0302.
    Misfire on 1 & 2. I web searched and the closest I found was someone reporting a
    simultaneous misfire on 3 & 4 on NASIOC (I think for a WRX). They think it was
    caused by going to high revs too soon. Mine seemed to occur coincident with high
    revs just after a warm start (entering traffic). It hasn't come back, but then I haven't
    given it much time.

    As simultaneous misfires a common Sube thing? Any thoughts? The car is running
    strong & smooth.
    David, Jul 30, 2004
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  2. David

    Jim Stewart Guest

    This is just a wild-assed guess...

    The way the coil pack works is that one coil is shared
    by 2 plugs. The current has to travel through both
    plugs and plug wires every time one plug fires. Seems
    to me that an intermittent plug or wire problem might
    cause a simultaneous misfire, assuming that the two
    missfiring cylinders are on the same coil.
    Jim Stewart, Jul 30, 2004
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  3. David

    David Guest

    Thanks! I wondered what was shared between 1&2, and 3&4. That sounds
    very likely. If it returns, off to the dealer, else I'll ignore it.
    David, Jul 30, 2004
  4. David

    Jim Stewart Guest

    Note that my description above is not totally accurate.

    Even though one coil is shared by 2 plugs, they don't
    "light the fire" at exactly the same time. At the instant
    that one plug fires on the compression stroke (and lights
    the fire), the other fires into the exhaust stroke.
    An intermittent wire or plug still might cause your
    problem though.

    Let us know what you find out.
    Jim Stewart, Jul 30, 2004
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