I replaced three of my park plugs today. My truck has over 100,000 miles and I didn't know when they were changed last.

Anyhow, the plugs I pulled out were NGK TR55-1GP (in an American truck!?!?!). I replaced them with Motorcraft SP498 plugs. I also replaced the wires (Prestolite?) with Motorcraft wires.

My question is on the NGK plugs, there is a small brown burn mark on the insulator around the center electrode.



It's only one small spot on each plug, otherwise they look fine. What could that be?

I'll tackle the remaining plugs (passenger side) this weekend.

 

Stick with Motorcraft, 4.0l OHV or SOHC eat other brands.

Looks like the it could be a flaw in the NGK plugs when used in a Waste spark system, 3 of the spark plugs will spark from + to - and 3 will spark from - to + thats waste spark
Ford uses 3 coils(in coil pack) to spark 6 cylinders, so the two spark plugs on one coil are hooked up in series, +.....-.....+.....- and both plugs spark at the same time, one cylinder on power stroke(normal spark timing) the other on exhaust stroke(wasted spark)

 

how was your mileage on those NGK spark plugs

i was extensively googling last evening and i discovered that the NGK plugs work better than the motorcraft SP-498 factory spark plugs

are the motorcraft spark plugs working better than the NGK ones

need some info here

 

Damn, I forgot about this thread.

I got all the plugs changed, wires too. All Motorcraft now.
It definitely idles better. It's almost silent while sitting at a light. I keep forgetting to reset my trip odometer so I'm not sure about the mileage, but is does seem to be doing better. I was getting around 13 in the city with the NGK plugs.

 

so are you actually getting better fuel economy with the motorcraft plugs versus the ngk plugs

 

Good thread here with pictures: https://www.ranger-forums.com/4-0l-o...0-sohc-119625/

Not that I ever thought about it but because of the waste spark system Factory used two different spark plugs, 3 with stronger tips and 3 with stronger electrodes, they are buying thousands so this saves money.

And IMO this is why some "other" brands might not last as long in the waste spark system, and why there can be confusion with part numbers.

Basically you want to use the double platinum SP-440, strong tip and strong electrode, so it doesn't matter which cylinder it goes in.

If another brand was also double platinum it may work as well


I would say you would have to get better MPG if all cylinders were firing normally, a misfire or even partial fire doesn't burn up all the oxygen in the cylinder, this oxygen is dumped into the exhaust system....................which is where the O2 sensors live, lol.
O2 sensors read oxygen levels, high oxygen = lean, so computer adds more fuel
So not only do you get slightly less power from a misfire, you also use slightly more gas because of it, double whammy