A mini spark plug tutorial if you have questions about the specified plug to use, or what the differences in plug design means.

I use Motorcrafts specified fine wire iridium enhanced center electrode with platinum ground side wire plugs, in both my 99 Ranger & Wife's 2000 Neon waste spark ignition system, as well as in my 94 Taurus 3.8L conventional distributor/single coil ignition system, as getting to the rear bank one plugs is a bit of a PIA on the 3.8L sidewinder engine, so at my age I don't care to do it any more often than necessary!!!! lol

The fine wire iridium enhanced/platinum plugs electrodes don't erode as fast in our engines & last a lot longer with the coilpack waste spark ignition system, in which the passenger side bank 1 (firewall bank on sidewinder engines), gets a reverse polarity spark, which emanates from the spark plugs ground lug/sidewire, to the center electrode, so that side wire needs platinum to slow spark gap/electrode erosion. Cylinder bank 2, driver’s side (radiator side on sidewinder engines) gets a normal polarity spark, which emanates from the spark plugs center electrode to the sidewire/ground lug, so its center electrode needs a platinum or iridium enhanced electrode.

The waste spark ignition system also works its coil pack, spark plug & plug wires Twice as hard as the single coil ignition system, as the waste spark system fires its plugs on Every rotation of the crankshaft, once on the power stroke, then again on the next rotation of the crankshaft on its exhaust stroke (waste spark).

On our waste spark V6 engines, the coilpack only has three coils to fire six plugs, so the plugs are paired together, such that when one plug is fired on its power stroke, its companion plug is being fired on its exhaust stroke (waste spark). So, in waste spark ingition systems, half the plugs get a normal polarity spark which emanates from the plugs center electrode to the ground sidewire, while the other half get a reverse polarity spark that emanates from the ground sidewire to the plugs center electrode.

The fine wire plugs also require less voltage to fire, so that helps on cold winter starts, when battery voltage is at its lowest because its cold, having to run the starter motor, fuel pump, ignition system & any other electrical load we have turned on. So, with that lower operating voltage the ignition system is having to work it's hardest to make a good hot spark to get us going.

On my 99 Rangers 4.0L waste spark ignition system, the passenger side/bank-1, got the factory PG = Platinum Ground spark plug, as that bank got the reverse polarity spark. (This special type single platinum ground/sidewire plug, was only available to the factory) & was only to be used in bank one, that got the reverse polarity spark, so that’s why it was to be returned to that bank if removed. The Rangers special factory non platinum center electrode, platinum ground sidewire (PG) plugs were eroded .008" out of Max spec on spark gap at 30K miles & this was after I had removed them when new & gaped them to the Min side for spark gap!!!! SO, in effect the spark gap had opened up .012" in only 30k miles on these special factory single platinum ground sidewire (PG) plugs!!!!! Not good!!!

Note: On single, or double platinum, or Fine Wire center electrode iridium enhanced plugs, with platinum pad side wire design, Use a Wire type spark gap gauge to adjust spark gap & Don't pull the gauge through too tight a gap, so as not to damage the platinum pads, or fine wire center electrodes.
I use a go/no go kind of feel/check by selecting a wire gauge that's .001" larger & smaller than the gap I'm setting. The .001" smaller / thinner gauge will go through Without drag, but the .001" oversize gauge won't go, so I know the gap is set exactly where I want it, without having to pull a gauge through the gap, thus likely avoiding any damage to the platinum pad or fine wire center electrode.

Also, while we're thinking about spark gap, if you use anti-seize on the plug threads, I'd suggest setting your torque wrench to the Min plug torque value, to allow for the anti-seize lube effect & not over tighten the plugs & mess with the gap you just took the time to carefully set.

I like to gap my new plugs to the small side of spec, as the gap is always eroding / opening up, so the spark gap stays in spec longer.

The smaller gap also helps a little on those really cold winter starts, as it's easier to jump the closer gap & it'll make for a hotter spark kernel to light things off, when battery & ignition system voltage is at its lowest & the engine & fuel are cold, not optimum light off conditions.

Back to plug type thoughts. Bank-2/drivers side, from the factory, got the single platinum (P) plug that had a platinum center electrode, as it got the normal polarity spark that emanates from the center electrode, to the ground/sidewire.

The specified Replacement Double Platinum plugs (PP), can be used in Any cyl bank, on Any type ignition system & its electrodes will last Longer than a regular copper core non platinum, or single platinum plug.

The fine wire iridium enhanced center electrode/platinum side wire design plug, will last longer than the double platinum plug, as iridium has a much higher melting point than platinum, so it's finewire iridium enhanced center electrode, erodes at a slower rate, while providing an easier to fire & more concentrated, hotter/higher temp spark kernel, to get us going.
I have notably faster year round starts in all three engines, with these plugs.

As has been said, we can use any plug design, as long as it's the correct heat range & it'll work in any engine, it’s just that the double platinum, or fine wire iridium enhanced center electrode plugs electrodes will last a lot longer & their spark gap will stay in spec longer.

SO, imo to get easier/faster starts which makes it easier on the starter motor, battery & ignition system & not having to replace that sidewinder Taurus rear banks plugs as often, it's well worth investing in the slight cost difference/increase in purchasing & installing fine wire iridium enhanced spark plugs.

On the wife’s Neon, I recently caught the Autolite fine wire iridium enhanced/platinum ground sidewire plugs at 1/2 off at Advance Auto + Autolite has a $2 ea. rebate that’s still on until later this year 2011, so mine at 1/2 off + rebate, were about $2.25 ea., a danged steal!!!! As I mentioned above, it too has noticeably quicker year round starts.

More spark plug thoughts for pondering.

 

More spark plug input from Autolite, Tech Specs (autolite.com) Some interesting info on multi-electrode ground design type plugs, plug metallurgy, heat range testing, use of anti-seize compound, plug wire info, etc., that might be of interest .