Which plug is bad?

I think the ground electrode is worn.
Rear bank of course.
My dbl platinum is single plat now

The right one.


And the better one is pretty shaky too

I removed coil pack to reach rear plugs and swapped 2 wires and had rough idle. Always something.

Neighborhood kids would occasionally decide to play a prank on my dad, switch the plug wires around on his truck , engine starting up the next day … rrrrrr … kerplunk kerplunk kerplunk … hiss… … lol … didn’t seem to phase him much. I guess he’d done that in his teenage years and knew the symptoms and how to fix it straight-away. Plug wires on my own truck are therefore numbered … lol …

It has canted valve heads and I was using a mirror to check left/right angle to put plugs in as it is firewall side and I could see an edge of valve thru plug hole? I guess I never really spend much time looking down plug holes but I am pretty sure I’m not supposed to see valve. Then it started with rough idle and I found plug wire issue. Seems to idle fine now. Maybe all is well?

Nothing unusual about seeing a valve through a spark plug hole on a modern day engine.

Now if you’re working on a Ford flathead…

Valve does move at angle.

Seeing a valve is not a big deal. I hope you replaced those worn plugs while you were in there - that job is too much of a PITA to do it twice.

Yes, new plugs. I unplugged all wires to get coil out and got them mixed up. 1 plug was very worn. Yes, the plug hole hole were I could see valve edge. The other plugs looked ok

I got another car. 180k miles. Seems to run ok. I pulled a plug and it has .070 gap. Electrode is about flush with porcelain. Spec is .035-.044 approx depending on brand of plugs. Were plugs changed at 100k? Or never? This is pic from pat goss’s garage. Looks like my plug.
All 4 were identical. 15 min job.

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Running engine with plug gap incorrect can stress the coils. Suggest to keep in mind if performance problem develops in future.