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

[Robert Deis]

On Wed, 30 Oct 2002, 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.

Yup, that was my first guess.  On my other turbo car, high-boost miss is
nearly always bad wires.  High boost race cars go with really big coils to
mitigate the problem.

> 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?

Something about high pressure from forced induction increases resistance
rather than reducing it- dunno why, but it always happens.

> 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.

But doesn't that test the system as a whole? It won't tell you whether the
problem is in the coil, distributor, or wire, just that one of the above
is bad-- which you already knew by the fact that you're missing under
boost?

I suppose it could eliminate mixture or fuel supply as a culprit, but I'd
think that would be easier done with an A/F and/or fuel pressure gauge..

--
------------------------------------------------------------------------------
  Rob Deis                  "Let the people know beforehand what the law
  MiB3347                      is and what they are to expect."
  rdeis at io.com                              -- 18th Congress, Rec. 75