[Mgs] fouled plugs Why?

[Paul Hunt]

Sounds like they weren't firing.  If this loss of power occurred while *other*
than someone having had the plug leads off for any reason then it could be the
cap breaking down (if the plug leads had been touched before this happened
then it is simply 2 and 3 reversed, the correct firing order is 1-3-4-2
*anti*-clockwise).  As plugs get older they become more difficult to fire, so
the HT voltage gradually increases over their life.  With a marginal cap this
can suddenly cause one or more plugs to stop firing, and changing the plugs is
the only apparent 'cure', even though they may well be well within their life
span.  I had this on my V8 for some time, the problem was being my daily
driver I always had to be somewhere when it happened and couldn't spend time
diagnosing, so had to keep a set ready-gapped in the car.  One day I *did*
have time to diagnose, and clipping a timing light onto the coil lead and each
plug lead in turn and watching it while cranking showed the coil lead flashing
as it should while some plug leads were flashing only occasionally or not at
all.  Changing the cap cured it once and for all.  Incidentally if this test
should show the coil lead flashing as it should but none of the plug leads
then it could be cap or rotor.

PaulH.
  ----- Original Message -----
   Deductive reasoning and process of elimination revealed that the two middle
spark plugs were not firing, were blackish and smelled like fuel.  I replaced
the two ugly plugs with new spark  plugs.  Other plugs are ok.