5.0L waste spark?

[koda2000]

I remove the spark plugs from my daughter's 2000 Monty 5.0 today. They were Autolite double platinum's and had around 80k on them. They were almost new when I bought the truck back in 2012, and I had checked and re-gapped the plugs to .54 thousands at that time. Since then my daughter has driven around 70,000 miles.

The truck still had it's original OE plug wires, which I replaced yesterday, and the truck had been running like a Swiss watch until a few weeks ago, when it developed a noticeable miss. I expect the new spark plugs to arrive from RA tomorrow, or maybe Tues.

Here's what has me puzzled. The CEL had reported a misfire on cyl 6 and had earlier reported multiple misfires w/out the CEL having come on. I decided to pull the plug from cyl 6 first. Holy crap! The gap was about .80 thousands. Then I pulled plugs 5, 7 and 8. They were all .80 thousands. I'm pretty sure this has a lot to do with the misfires. Then I pulled plugs 1-4 and they were really in good shape, measuring maybe .55-.56 thousands.

Does the 5.0L use a waste spark on bank 2? Is that why all the plugs on bank 2 were so worn while bank 1 plugs were not? I don't recall seeing this on my 2001 Expl 5.0L when I changed its plugs.

 

[J_C]

I don't have the 5.0L, but if it has only 4 coils then it has to use the waste spark system, which as I understand it means that the spark travels from ground to the electrode on one bank of plugs and from electrode to ground on the other banks' plugs, which could cause more wear on the plugs in whichever bank have the electrode at the receiving end of the spark.

Double platinum should have helped, but still... 80K mi is a fair run for waste spark plugs that fire twice as often.

 

[1998Exp]

Does the 5.0L use a waste spark on bank 2? Is that why all the plugs on bank 2 were so worn while bank 1 plugs were not? I don't recall seeing this on my 2001 Expl 5.0L when I changed its plugs.

Here is my understanding: wasted spark occurs on both sides of the engine, because the coils fire on every revolution of the crankshaft. The "wasted" spark goes through exhaust gas, which contains a lot of water, and thus has low voltage, around 2kV. The "real" spark is across the combustible mixture, and at around 20kV. The coil generates the voltage to sustain the sum of the two, so about 10% of its energy is "wasted". Because the two plugs that are firing simultaneously are in series, the direction of current is opposite: on one side it's from the center electrode to ground; on the other it's from ground to the center electrode. The current carries metal particles along. Thus the different erosion pattern. "Double plats" are supposed to minimize the erosion, but ultimately the plating wears out, and when that happens, the side of the engine in which the current flows from the center electrode to ground suffers more, because the center electrode is much thinner. Look at the photo in this posting, from a Ranger What would cause differences in spark plug wear on a '97FordRanger?

 

[koda2000]

@J_C and @1998Exp

Yes, that photo link provided is exactly what I'm seeing. I thought the platinum plugs were supposed to last for around 100,000 miles and the double platinum's should have held up better than the OE single plat's. I was planning to replace them at around 75k, but with this amount of wear on the bank 1 plugs I guess I should replace at least the driver's side plugs at around 50k... ? As I said, the bank 2 plugs looked really good at the same mileage.

IIRC when I changed the plugs in my '01 5.0L Expl (at 179k) the plugs I removed looked a bit worn, but both banks looked pretty much the same. Of course I have no idea how long they had been in there.

IDK, live and learn I guess. I wonder what the plug maintenance interval says in the owner's manual? Thanks for the replies.

 

[1998Exp]

My '98 manual specifies 100,000 miles plug replacement. If memory serves, the OEM plugs were single platinum, but two different kinds: platinum on the tip on one side of the engine, platinum on the ground electrode on the other. About $0.25/plug saved, compared to double plats. Multiply by 6 or 8, and by the number of vehicles they built over the years with this system, and pretty soon you've put aside a pretty penny... Don't believe anyone (including Motorcraft) sells those weird plugs with platinum on the wrong end anymore. And of course, the wasted spark approach has gone the way of the dinosaur, replaced almost two decades ago by the coil-on-plug system (which, incidentally, does just fine with single plats, because all plugs fire the same way).