Yep... that's what I'm describing... In this system, there are two spark
plugs attached to one coil. These are paired in what is known as "running
mates".... When one cylinder is coming up on compresion, it's running mate
is coming up on exhaust. Both spark plugs "fire" (I don't like that term,
but it gets the point across) at the same time. For the cylinder containing
a "working mixture", this is good... for the cylinder that still contains
spent mixture, it doesn't mean anything.
Waste spark systems have some unique considerations.... a little complex to
go into without tuerning this posy into something that will lose people
quickly... Suffice to say that there are times where coil concerns can
affect only one sylinder.
On these systems there is always one "poitive" plug and one "negative"
plug.... The spark never changes direction. The big benefit(s) of the
platinum plug is first, reduced material depletion.... each time a spark
plug "fires", a small amount of material is eroded from the electrode. It
doesn't deposit on it's counterpart since combustion chamber currents carry
this material away. Gap ionization (and therefore spark path) is "easier" to
create from a sharp corner than a rounded corner (please don't ask why - I
tired reading up on it but I keep falling asleep). The design of the plat
plug always presents a sharper corner than other materials simply because
the electrode is so skinny.
With this is mind, there is little sense in installing a plug with only one
platinum electrode in one of these systems. While we will reap the benefits
on one half of the motor, the other half of the motor will not see any of
the benefits... Combustion efficieny can suffer and runing concerns could
emerge. Given that spark plugs are now expected to live well beyond the
warranty period, the manufacturers have little concern over what hapens....
<firstname.lastname@example.org> wrote in message
> Jim Warman wrote:
> > For your EX.... it has a "waste spark" ignition system.... the spark
> > on one bank fire from centre to ground and, on the other bank, ground to
> > center. If these spark plugs are the originals, you will notice that the
> > plugs from one side will look different from the other.... one side will
> > have AWSF??PP and the other side will be PG. If you can't get double
> > platinums, settle for the lower cost copper plugs.
> Interesting. I hadn't heard of this, but it makes sense. See "Figure 5
> Typical distributorless ignition schematic on this page":