2nd cracked spark plug - why?

[TLC2013]

Good to hear you got to the bottom of this. Thanks for the update. I replaced mine at 100k and was suprised by how filthy they looked. Do you have a picture of yours at 150k?

 

[bloc]

If a cylinder runs lean it can do that. Maybe you have a dirty injector. Haven't seen that on the 200 before.

Could have also been a bad batch of plugs, but I'd guess clogged injector causing detonation.

Wouldn’t the ground strap show evidence of detonation if it was bad enough to crack the porcelain?

 

[kcjaz]

Good to hear you got to the bottom of this. Thanks for the update. I replaced mine at 100k and was suprised by how filthy they looked. Do you have a picture of yours at 150k?

I can’t find #8. I thought I threw all of them in a box but 8 went AWOL.

 

[40Man]

Wouldn’t the ground strap show evidence of detonation if it was bad enough to crack the porcelain?

Yes. The ground strap on his #6 plug appears to show evidence of a lean condition, but hard to tell from the pic.

 

[kcjaz]

Yes. The ground strap on his #6 plug appears to show evidence of a lean condition, but hard to tell from the pic.

#6 looks pretty dark on the strap to me and the point is also dark in color. I thought a "clean" or white spark plug was the tell tail for the cylinder running lean.

 

[40Man]

#6 looks pretty dark on the strap to me and the point is also dark in color. I thought a "clean" or white spark plug was the tell tail for the cylinder running lean.

A slightly lean will be clean generally. A very lean condition will look similar to #6 above. Here is a handy chart.

 

[kcjaz]

A slightly lean will be clean generally. A very lean condition will look similar to #6 above. Here is a handy chart.

View attachment 2749879

Very useful! thanks

 

[Lester did that]

So, I think the moral of the story is don't go 150K miles on a set of plugs. And if you do, carry spare plugs, a spare ignition coils (or 2), and tools.

For 150k that's not bad looking. No plug will be pure and clean after 150k. A chart like the one posted is great.

A good rule of thumb going forward is if one plug goes bad replace them all. Now if you recently replaced them all and the same one goes bad again before the others then you need to do a little trouble shooting to get to the problem.

Your correct on the ignition coils. I have a 2009 LC that I replaced the plugs on. 165k ish and the plugs where replaced once at 75K. Some where hard to remove. I also picked up 2 ignition coils just in case. Ended up breaking one just because of age or my heavy hand. Returned the other one. So having an extra ignition coil on hand just in case is advisable. Return them if you don't need them.

 

[vegasfj40]

I had gotten a bad OE spark plug once for my 95 FZJ80. Was surprised when I removed it, the plug had a tiny hairline crack in it. The dealership gave me a new one and problem solved. Its possible maybe it was dropped during shipping or packaging. I would never put 150k on a set of plugs.