Bosch Plat. plug HR9BP plug with about 10K miles on it out of my 88 L98. Engine uses a quart between changes at 3000 miles or so, gets 24 mpg (with clean plugs) and run fine normally. What happened to this plug? Haven't pulled the others, this one was enough. Is this common with the platnum plugs, wrong plug maybe, or something else? Any comments appreciated, but looks like it's time for a set of AC plugs.

 

Holy %*@&!!! I'd be pulling the rest of them to see if its common to all of them (can't imagine it would be or the thing wouldn't run at all).

 

Are you sure the spark plug had the right heat range for your engine?

 

Believe it or not the engine ran pretty good, little rough at light throttle low rpm. About fell over when I saw this plug. Thinking now maybe bad valve seals or guides, or both. Deposit is hard as ceramic, oil getting on the plug cold then baking hard maybe. Might be a winter project, pull top end and redo heads, or replace with some aluminum heads. Good time for a set of headers too. Getting into some real money though. Maybe a set of AC plugs first, see what happens.

 

I had a set of Bosch platinums go bad as well after only 2000 miles. I did not let them get to the death stage as that plug but I would imagine mine would have looked the same if I had left them in there any longer.

 

Id throw them out just because theyre bosch plugs. I had a set and they stayed bone white and nice and clean but in another car that used oil they seemed to be more easily fouled by oil then standard plugs.

Also, whats the gap on that plug? Looks like the ground electrode is really far away. Maybe its an illusion since it has crap all over it.

 

Had the same issue with my bosch's in my LT1 a few years back. Switched to delco's never had the problem again.

 

That's one moldy plug!!

I too am curious how spark traversed the gap. I agree, ditch the Bosches and get Delco. hey, at .99c, what's not to love?

 

Update. Rest of the plugs looked better, but still not right. One plug was really white with a groove burned down the center electrode/ceramic. Others were white on one side, black and crusty on the other side. Replaced the valve seals (o-rings) on that one cylinder with the crusty plug, easy to get to, and new AC plugs. Thanks for your replies.