Gray Plugs

[rr]

With Bruce being off-list for a couple of days, I'll add what I can. Mild
detonation can show up in a number of ways. I've seen it as nothing more
than a light dusting of black specks (carbon blown off chamber walls) on
a pure white insulator, to light audible knock. Sometimes a loud exhaust
can mask audible knock. A roughness in the engine can also be a sign
of light detonation.

What I think is happening here, is that audible knock is being covered
(smothered) by excess fuel. I've seen this before where the fuel pressure
was a bit high (carb & too rich), and timing was added until it felt good.

It was a number of years ago that I last saw this, and at the time did not
know what to think of it (the gray plugs). I remember checking the timing
this guy was running & backed it off. Then checking the fuel pressure & adjusted
it to a proper value. He constantly over-revved the engine & shortly thereafter
cut the block in half (Pontiac 389). I think what Bruce is saying below (change
in chemistry) really explains this case.

I do know that after the adjustments the engine ran much better. In closing
I would tend towards the gray plugs as not detonating. However, it is showing
that a problem does exist.

BobR.

p.s. speaking of plugs, what is the reason for 'spider webbed' plug insulators?

Mitch Louole wrote:

> Is this another way of saying,.. Detonation was occuring,  albet in a mild
> state?
>
> >From: "Bruce Plecan" <nacelp at bright.net>
> >Reply-To: gmecm at diy-efi.org
> >To: <gmecm at diy-efi.org>
> >Subject: Gray Plugs
> >Date: Thu, 3 May 2001 14:48:23 -0400
> >
> >
> >The info is from another list, but thought was worth mentioning here.
> >
> >Gray plugs
> >
> >I think most of the experienced plug readers know it's a timing (and often
> >a
> >slight fueling issue), BUT it represents the change in chemistry in the
> >combustion chamber from detonation.
> >
> >HTH
> >Bruce
> >
> >
> >----------------------------------------------------------------------------

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