Scope pics...

[David Cooley]

Couldn't say if fords do something different except for the plugs...
I do know on my GN, if the plugs stayed in for 30K or so (when I first got
it and it was stock) the center electrode of 3 plugs had more wear that the
center of the other banks 3, and the ground of the 3 with minimal center
electrode wear did have a good bit more wear than the 3 with the center
erosion.

Fords service manuals try to explain the single platinum plugs as being for
reducing wear due to the DIS polarity... when you replace the plugs, they
say to use double platinum.


-----Original Message-----
From: owner-gmecm at diy-efi.org [mailto:owner-gmecm at diy-efi.org]On Behalf
Of Bruce Plecan
Sent: Monday, November 13, 2000 9:58 PM
To: gmecm at diy-efi.org
Subject: Re: Scope pics...





> And if you look at the secondary waveform on a scope, it oscillates in the
> same polarity from 0 to say 15KV or whatever value it hits...
> it never reverses it's polarity.

Contrare, It's swinging across the 7.5KV.
It would be more apparent if one side of the secondary was at ground, then
the open voltage could be compared to ground but since it isn't, the ground
element reference to the secondary is lost (DIS lost spark).

The air gap, when it ions and *fires* sets a voltage based on the conditions
in the combustion chamber.  I say fire to make it a distinct event rather
then  a generic term such as spark.  A normal spark for a .030"  is alot
less then in a combustion chamber.

> Look at what Ford does with their DIS cars... one bank of the engine gets
> plugs with a platinum tipped center electrode, the other bank gets plugs
> with a platinum pad on the ground electrode... Because the voltage/current
> flows in ONE DIRECTION thru the plugs.

Mind splaining why in the GN they all burn the same?.
As far as I know, and I'm a few years behind on saying this, all the DIS
stuff uses the same plugs anywhere within a specific engine, in the GM
family line.
Not a slam, but I haven't seen any Ford ignition electronics that are really
grand
I also, don't know or even have a clue if ford isn't doing somethin strange
like opening the primary power, or both sides of  the primary.

> At 06:29 PM 11/13/2000 -0500, you wrote:
> >All of this talk about currents when the discussion is of a voltage wave
> >form and not of a current wave form which is considerably different.
> >Remember that a coil is an inductor and that the response of an inductor
> >is to oppose the change in current through the inductor so that when the
> >points are closed the current flows through the inductor creating the
> >magnetic field of stored energy,  when the points open the inductor
> >reverses it's voltage and amplifies it's voltage in an attempt to keep
> >the current flowing in the same direction and at the same rate until the
> >energy in the magnetic field is used up.

Opening the points, stops the electron flow.
So no electron flow, no voltage in that respect, no *reverse voltage*.
Electron flow at that point is from the field collapsing, and generating an
electron flow.
If we want to get to just theory then we need to define if we're working
with a primary that is like 6 trillion mile long or infantesmally short one.
If the primary was 3 valances long then the voltage would be about
instaneous in what ever it did, depending on material would be exchanging
one ionied particle for another.  And no reversal, just a transfer of one
electron.

 This inverted spike is
> >precisely what is used in the ingnition coil although further amplified
> >by the step up to the secondary coil.  These segments of the points
> >being on or off and the different parts of the reaction are all A/C
> >components that have frequency that readable by a tach, but the actual
> >spark across the gap of the plug will work in the same direction each
> >and every time.

So it goes from A/C to D/C just cause there is an air gap?.
That doesn't make sense to me.

Thus the current through the spark plug, which is only
> >during spark, is always going in the same direction.

Can you show me this, in the erosion of, plugs if I sent them to you?.
Theory is fine, but when the real world doesn't support it, the theory comes
into guestion in my book
Bruce


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