What's wrong with this spark plug? (burn marks on center electrode)

[Boyd McDuffy]

A/C Delco for me since my 1990 was brand new.

 

[Tom P]

That's what I'll order then.

So far the idle is still WAY better than it was, but there's still some lingering shake that was definitely not there before I put in the Delco coppers. It's possible my coil is getting weaker and it's not the plugs' fault, but finding that one messed up plug in a cylinder that has not been fouling anything up make me suspicious.

IF you haven't done so for a while, change the spark plug wires. I chased a gremlin for a similar issue for a long time and when I replaced the spark plug wires I found that a couple of the wires had compromised jackets and I was probably loosing voltage through that. Unless they are new or less than a year old I'd think about replacing them. Changing the coil wouldnt be a bad idea either. You can get a lot of this stuff off of amazon for a really reasonable price and you can usually choose from AC Delco or Delphi and pay less than the Parts store brands. The Coil for my 7.4 was like 23 bucks. Cheap insurance.

 

[redfishsc]

I do have new plug wires, they are about 8 months old. However, at the time I was swapping the intake gasket and several other things, and didn't really put much thought into it, and put cheap Autozone wires on it.

I would imagine the coil for the 7.4 could be the same coil. I'll look it up. $23 is cheap insurance.

 

[redfishsc]

Yep, it is only about $30 depending on the brand you get. I'll probably try a Denso if better plugs and wires don't help it.

It definitely is idling better than it was since I swapped out that one damaged plug, but it's still occasionally sorta twitchy. Much more than it was a year ago.

 

[Tom P]

Sounds like a plan. The ignition system on my truck is pretty much all new in the last year (minus the IGN control module and distributor base) and it starts and runs flawlessly now. Good luck and hopefully a solution will present itself to you.