Found this old pic of a spark plug I pulled out of my truck right after buying it, many years ago. They were all like this, worn down to the nub. The previous owner complained that he was only getting 9 mpg, so I used it has a bargaining point. LOL

Mileage jumped to roughly 14-15 right after changing em. Surprisingly, the 4.7 ran well even with the huge gaps.

 

Coil-On-Plug makes a BIG spark.

Racers have compared the LS stock COP coils to a 20-amp magneto.

Most of that comes from having 7 times the dwell time to build up a charge before firing.

On a V8 distributor turning at 3,000 RPM, there are 50 rotations per second, or 400 coil sparks per second (0.0025 of a second between coil sparks)

On a V8 distributorless turning at the same 3,000 camshaft RPM, a single coil sparks only 50 times per second (0.0200 of a second between coil sparks)

It doesn't seem like much, but that built-up spark can jump a LONG ways.

I'll see your worn tip and raise you missing electrodes. The one missing completely went 6.05 @ 235 MPH, it was firing off everything but the electrode (melted a piston & tore up the cylinder head). Those signs didn't show up on the bore scope, but the next two runs screamed "There's an issue, stop!"

https://photos.app.goo.gl/G86NVboMPnwH3ffeA



https://photos.app.goo.gl/1sEEy8MHQggE7RZ97



https://photos.app.goo.gl/8WZVkHL1aXuC4DMW8

 

What caused those plugs to fail like that? Did the tips burn off or break off?

 

Wear, just from being used. Every spark wears a little bit off the plug.

 

When I bought my escape the plugs were worn down to basically nothing. Makes me wonder just how much extra gas the previous owner blew just to save a $100 on new plugs.

 

Not sure if replying to Vity or I;

We found a fuel leak that was leaning the engine way out to the tune of a 1400 degree EGT. Those electrodes were gone by 330 feet; the last 2 runs were aborted at 3.5 seconds into the run, hence some strap left. The one that's completely gone was 6.05 @ 235, a full pull.