What the hell did I blow up this time? The answer and now another question

[Robert Myers]

You are missing the scientific fact that an arc is more easily produced at
low gas pressure than at high gas pressure. That is why neon lights have a
partial vacuum inside them rather than a higher than ambient pressure. Loss
of voltage at the plug (from whatever source the loss might come) can lead
to a high boost stumble or misfire while the engine will run at idle or low
power output levels quite nicely.  Those losses can come from a variety of
causes.  These can include things like high tension line insulation
breaking down and leaking voltage or from a weak coil, etc.

At 11:13 AM 10/30/02, SJ wrote:

>I have often thought about this problem . . and how to diagnose it.
>Similar problems occur when you have old(high resistance) sparkplug wires.
>The problem is manifested by missing(bucking) at heavy engine loads. Idling
>and low engine loads does not result in missing.
>
>I can understand what happens electrically  . .the voltage drop across the
>high resistance wire results in less voltage across the spark plug . .. and
>it does not fire. But . . . .one would think that a richer air fuel
>mixture(under load) would result in a lower resistance for the spark. So why
>does the plug fire ok at low loads and miss at higher loads??  What am I
>missing here?
>
>There must be some physicists in the group that can explain the phenomenon.
>
>As far as diagnosis of a weak spark, I would think one could use an
>oscilloscope with a special high voltage probe. Then you can read out the
>voltage directly from the vertical scale. But, scopes cost big bucks.
>As an alternative, I would think that a test spark plug gapped to reflect
>the required voltage for jumping a gap at normal atmosphere would work. For
>example . . .0.070 gap for firing by 34K volt coil. If the coil was only
>putting out 25k volts . . the test plug would not fire. I'm sure there are
>variables involved, like atmospheric pressure and humidity.
>
>At any rate, this is a common enough problem to merit discussion on simple
>diagnostics.
>
>SJ
>88 5kq
>90 100q
>
>
>
> > Subject: Re: quattro digest, Vol 1 #4128 - What the hell did I blow up
>this time? The answer and now a question
> > From: Larry C Leung <l.leung at juno.com>
> >
> > Jim, List;
> >
> > Glad you were able to figure things out (although no thanks to me...)
> >
> > How does one check the coil anyway. I have bogging issues at considerably
> > less
> > levels of boost, although it's intermittent (though more often than not).
> >snip<
> > I was wondering how to test the coil other than the laying of the
> > plug on the head
> > and watching the plugs for spark. I do get a spark when I do that, but
> > somehow I can't
> > imagine it's a test for when the CC is under 10 - 12 psi of boost.
> >
> > TIA,
> >
> > LL - NY
> >
> >
> > > From: JShadzi at aol.com
> > > Subject: Re: What the hell did I blow up this time? The answer.
><snip><snip>
>
> > >
> > > > I figured it out,  BAD COIL!!!!!!!  Whew, that was a
> > > > close one.  I guess the coil just decided it didn't
>
>
>
>
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Bob
*****
  Robert L. Myers   304-574-2372
  Rt. 4, Box 57,  Fayetteville, WV 25840 USA   WV tag Q SHIP
  '95 urS6  Cashmere Grey - der Wunderwagen    ICQ 22170244
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