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

[SJ]

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