[Diy_efi] OT - platinum plugs burning up wires

Mon Sep 12 14:06:15 UTC 2005

What you mention about a comparo is a great idea; I
only wish I had an analyzer (remembering the days of
the 'SUN cabinet' unit that had a scope that clipped
to the common coil wire and a sync lead off plug #1,
would show the relative firing current in each
cylinder. Many times I found wire problems causing
misfire as you describe (fishbites) by comparing the
per-cylinder spikes and focussing on the peaks and
valleys, peaks generally were the culprit as the
resistance climbed in a bad wire causing the spark
voltage to climb, often to the point the coil couldn't
overcome it and therefore no spark t'all.

So, does anyone have access to a scope that wants to
try looking at different plugs in a couple of
cylinders and comparing? I've built the sensors in the
past and would be willing to suggest how if someone
has a DC powered scope and the incling to test and
post results. Might be a interesting project, I just
don't have the equipement anymore to do this with.

--- David Allen <davida1 at hiwaay.net> wrote:

>   The internal resistance is for radio interfarence
> supression and for
> interference on the engine electronics.  Some
> distributor rotors have a
> resistor in them to suppress RFI at the distributor
> rotor-to-cap spark gap.
>   Most modern plug wires are actually resistive in
> and of themselves. A few
> have copper wire with a resistor built into the plug
> boot. Most are
> "supresion core" wire.  Instead of a copper wire,
> they have a core made of a
> graphite material.  A normal length plug wire may
> have several thousand ohms
> of resistance.
>   There are two main ways in which these fail.
>   The graphite core can develop a small gap due to
> mishandling, age,
> improper installation of terminals or a combination
> of factors.  Each time
> the ignition systen fires through this wire, there
> is a small spark across
> this gap.  The plug still fires.  Each spark
> vaporizes more and more of the
> core creating a longer and longer gap. Eventually
> this gap is too much and
> the spark no longer jumps the gap.  You get a
> misfire. This is particularly
> noticable under low RPM high load conditions like
> climbing a gentle hill in
> high gear.  Gives a "fishbite" symptom.  You can ohm
> out the plug wire and
> it will show infinite resistance.  May have a
> visibly swollen or soft area.
>   Second common failure is insulation breakdown. 
> This happens when the
> insulation gets damaged by age or heat or excessive
> voltage due to a
> disconnected spark plug or burned away graphite
> core.  The insulation is no
> longer able to contain the voltage and a spark jumps
> from the side of the
> ignition lead to a metal part of the engine. Once
> this happens it will
> repeat because the inslation becomes conductive
> after being penetrated by a
> spark, and burned or carbonized. Visible arcing, and
> burning of insulation
> is evident.
>   When a coil fires, it sends out a pulse of
> current.  The resulting voltage
> level is a function of how much resistance there is
> in the circuit and how
> wide and how many gaps it has to jump (plus other
> factors).  The less
> resistance in the circuit from the coil to the plug,
> the less the voltage at
> the coil during each spark.  If the core of the plug
> wire is bad, the cap
> and rotor are worn out, or the plug gap is too wide-
> the insulation of the
> ignition coil and ignition leads can be subject to
> much, much more voltage
> than necessary.  This can lead to the second type of
> failure described
> above.
>   I would like to see a real scientific comparison
> of the firing voltage
> difference in a given engine at the same gap-
> platinum versus non-platinum
> plugs.  There are so many different systems out
> there it is impossible to
> know what can happen in every situation.  Possibly
> on a Hyundai the ignition
> system is under designed and close to its breaking
> point under normal
> operation.  Therefore, the small increase in firing
> voltage from platinum
> plugs is too much.
>   All I know for certain is- I haven't had any
> damage using them in my cars
> with Delco HEI and DIS ignitions.
>   Just my two cents worth!
> David
> 
> ----- Original Message ----- 
> From: hal sumption
> To: diy_efi at diy-efi.org
> Sent: Saturday, September 10, 2005 12:56 PM
> Subject: Re: [Diy_efi] OT - platinum plugs burning
> up wires
> 
> 
> Adding resistance to the circuit will lower the
> current and reduce the
> likelihood of burning the wires.  From what I
> understand, the purpose of
> adding resistance to the plug wires is to reduce
> radio interference they may
> generate.
> ----- Original Message ----- 
> From: Becker, Damon (Damon)
> To: diy_efi at diy-efi.org
> Sent: Friday, September 09, 2005 10:23 PM
> Subject: RE: [Diy_efi] OT - platinum plugs burning
> up wires
> 
> 
> Some plugs have internal resistance, others don't. 
> I was under the
> impression this is more to avoid burning up the
> coil, not the wires.
> 
> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org
> [mailto:diy_efi-bounces at diy-efi.org]
> On Behalf Of Geoff Harrison
> Sent: Friday, September 09, 2005 9:57 PM
> To: diy_efi at diy-efi.org
> Subject: Fw: [Diy_efi] OT - platinum plugs burning
> up wires
> 
> Rick, that does sound like bunk. Your leads may have
> been on the way
> out.
> The way I see it, doesn't make much difference what
> the electrodes are
> made of, only a small amount of current flows when
> the plug fires. The
> gap has more influence on the current, and never
> enough to burn out a
> lead.
> My question is, did the dealer keep the plugs?
> 
> Geoff
> ----- Original Message -----
> From: "Rick McLeod" <dunvegan at sbcglobal.net>
> To: <diy_efi at diy-efi.org>
> Sent: Saturday, September 10, 2005 12:59 AM
> Subject: [Diy_efi] OT - platinum plugs burning up
> wires
> 
> 
> Sorry for being off topic, but I know there is a lot
> of knowledge in this area on this list, and this
> might
> be of interest to discuss (remember the recent plug
> discussion?)
> Recently I had an issue w/ a Hyundai where the plugs
> were replaced w/ platinum at a tune up. A few
> k-miles
> down the road, the car began running poorly, and was
> taken to the dealer where it was diagnosed as having
> 'burned up ignition wires'. The service advisor
> stated
> that you MUST NOT use platinum plugs in these cars
> since it will cause this to happen.
> 
> My question is: What is different about them that
> would cause this, it sounds like 'bunk' to me, but
> am
> looking to the vast world of knowledge on this list
> to
> get some insight.
> 
> Thanks
> 
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