Not long after buying my car I did a bit of a health check on the plugs and noticed that the coil packs had a brown/red dust on them and some slight burn marks. I cleaned them down, refitted and forgot about it - car was running fine as far as I could gather.
A few days ago I checked them again, just part of a pre-trackday once over and noticed the red dust back and more burn marks, slight texture to the plastic too where they should be smooth.
I lathered them this time with dielectric grease and got on with the trackday, car ran absolutely fine all day.
I took them out again tonight and took photos. 4th is missing because it wasn’t really marked at all.
I’m now building up my winter tinker-list, so wondering if these should be added to the replacement list? Car is 2006 with 20k miles.
If I do replace them, anything I should do to prevent this happening again? I’ve mentioned in my other post about IAT’s that I’ve noticed my car being a bit “hot or cold” this year, nothing obvious as the car never fails to start/run normally - but sometimes under heavy acceleration it feels much ‘zingier’ than other times… could arcing coils cause that under certain circumstances?!
Confused, I thought they are made of plastic or rubber, in which case they cannot arc or trace. Looks much more like corrosion from elsewhere running down the outer case. Have you looked “down the hole” to see if you can see where it’s coming from. The other option is the brown is coming up from the plug. I’ve seen that and have always assumed a bit of combustion gas can get out round the plug ceramic.
Your first picture does look metallic and it looks like corrosion traces, ready to be corrected,
Arcing coils are definitely a thing, I’ve been electrocuted by a Clio before for brushing my hand across the top of the rubber HT leads I’m no expert but there’s a hell of a lot of voltage going through that part of the system, so any degradation at all to the rubber/plastic could break down it’s effectiveness as an insulator… I guess?
Cheers Winthattt, I’ve also been doing some googling - some interesting info on Corona Discharge.
I’ve found two different theories for cause of the brown stuff at the base of the spark plugs, one being the corona discharge as per the NGK article and one being your initial theory of combustion gasses leaking through the plug - NGK seem to strongly discount the combustion gas theory, but either way it seems quite common and ‘normal’.
As for my coil boots, the ‘damage’ that’s visible on the outside casing is quite high up and away from the base and sparkplug. I did some more googling on this and an awful lot of my returns are 2zz specific in either the Celica, MR2 or Lotus forums. Whether that’s just Google Analytics “knowing me” and being clever, I dunno.
The state of the coils is described very closely to how mine look: “the small black/brown spots were definitely burn marks and pitting where there had been arcing and intense heat” but this particular forum member was having real running problems with his car, I am not.
As I’m not experiencing any real running problems or EML’s I’m not going to rush to swap these, but over winter I’ll probably refresh them as part of my annual winter tinkering. I’m guessing that a lot of the posts above involving misfires, idle problems and EML’s are people who have had their coils in this state for a long time and the degradation has continued to the point that the spark plug isn’t firing properly. I don’t think I’m at that point yet, but the burn marks on my coils certainly suggest that energy is “escaping” in the wrong areas, so it’s certainly not optimal.
I’m no expert but there’s a hell of a lot of voltage going through that part of the system, so any degradation at all to the rubber/plastic could break down it’s effectiveness as an insulator… I guess?