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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 10-04-2012, 07:41 AM
kcornwell kcornwell is offline
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Need advice: One of my spark plugs is "gummy" (see picture)

My mechanic said these were the original spark plugs with 63,000 miles on the car. Should I be worried about the gummy spark plug?
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  #2  
Old 10-04-2012, 09:35 AM
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CALWATERBOY CALWATERBOY is offline
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Quote:
Originally Posted by kcornwell View Post
My mechanic said these were the original spark plugs with 63,000 miles on the car. Should I be worried about the gummy spark plug?

Yes.
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  #3  
Old 10-04-2012, 09:40 AM
The X Men The X Men is online now
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Looks like something is not right inside that cylinder.
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Old 10-04-2012, 04:18 PM
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DSXMachina DSXMachina is offline
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Quote:
Originally Posted by kcornwell View Post
My mechanic said these were the original spark plugs with 63,000 miles on the car. Should I be worried about the gummy spark plug?
No.
Put the new plugs in. If it runs good leave them in for 5K miles and check again. My informed opinion: the plug will be clean.

(Anyone else notice all that blow-by on the porcelain of all the plugs?)

Last edited by DSXMachina; 10-04-2012 at 04:20 PM.
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  #5  
Old 10-04-2012, 06:46 PM
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Originally Posted by DSXMachina View Post
No.
Put the new plugs in. If it runs good leave them in for 5K miles and check again. My informed opinion: the plug will be clean.

(Anyone else notice all that blow-by on the porcelain of all the plugs?)
Okee Dokee....why should it clean up?

Saw - looks like blow-by. How's that happen on 'em all?
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  #6  
Old 10-04-2012, 06:47 PM
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Quote:
Originally Posted by kcornwell View Post
My mechanic said these were the original spark plugs with 63,000 miles on the car. Should I be worried about the gummy spark plug?
Which cyl?
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  #7  
Old 10-04-2012, 08:37 PM
aleks001 aleks001 is offline
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Quote:
Originally Posted by kcornwell View Post
My mechanic said these were the original spark plugs with 63,000 miles on the car. Should I be worried about the gummy spark plug?
I could be wrong, but after that many km's I've never seen different looking spark plugs in any of the cars I've ever had. Looks pretty normal too me.
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  #8  
Old 10-05-2012, 08:58 AM
kcornwell kcornwell is offline
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Originally Posted by CALWATERBOY View Post
Which cyl?
Sorry, not sure which cylinder.
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  #9  
Old 10-05-2012, 09:57 AM
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Originally Posted by CALWATERBOY View Post
Okee Dokee....why should it clean up?

Saw - looks like blow-by. How's that happen on 'em all?
Because the plug is what was causing the poor burn and by replacing the plug he eliminates the cause of the fouling. In a situation where I have no evidence to the contrary I always go for the simplest explanation. It has saved me hundreds of diagnostic hours on very complex systems. I would install new plugs and have him drive it a few thousand miles, then pull the plug for another check. It's very cheap diagnostics because it means he doesn't have to pay a tech hours of labor to find a problem which may not exist.

The blow-by is due to a poor seal between the porcelain and the steel. We see a lot more of it nowadays and I think it's due to a change in the manufacturing process. It can get so bad it burns the inside of the boot, causes carbon tracking, and then a misfire. The deposits on these plugs don't indicate a critical situation yet, it can get much worse.
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Old 10-05-2012, 11:02 AM
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Quote:
Originally Posted by DSXMachina View Post
Because the plug is what was causing the poor burn and by replacing the plug he eliminates the cause of the fouling. In a situation where I have no evidence to the contrary I always go for the simplest explanation. It has saved me hundreds of diagnostic hours on very complex systems. I would install new plugs and have him drive it a few thousand miles, then pull the plug for another check. It's very cheap diagnostics because it means he doesn't have to pay a tech hours of labor to find a problem which may not exist..

Y'see? I glossed right over the NEW plugs...assumed same plugs reinstalled. My bad.

And, a good reminder to pull 'em now & then for inspection.
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  #11  
Old 10-05-2012, 03:08 PM
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...and another thing...notice the threads on the "fouled" plug compared to the rest. Also look very closely in the area between the seal ring and the base of the plug. What do you see? What is your theory as to why all the threads are dirty, and why there are deposits at the seal?

That's the reason this plug looks like it does.

The bill is in the mail. Now let me enjoy my weekend.

Last edited by DSXMachina; 10-05-2012 at 05:05 PM.
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  #12  
Old 10-05-2012, 04:02 PM
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galahad05 galahad05 is online now
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Running rich? That kind of doesn't make sense, what with O2 sensors and tight ECU control and all....
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Old 10-05-2012, 05:01 PM
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Originally Posted by galahad05 View Post
Running rich? That kind of doesn't make sense, what with O2 sensors and tight ECU control and all....
The ECM can tell which bank of three cylinders is too rich or too lean, and can kind of infer which cylinder it might be. The problem this plug experienced resulted in a condition for which the ECM could not make a sufficient short or long term adjustment in that cylinder.
So we need another possibility which is the likely culprit.
Hint: It was neither spark nor fuel, nor that the plug was excessively worn.
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Old 10-05-2012, 08:05 PM
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Improper gapping, maybe.
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Old 10-05-2012, 08:53 PM
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Quote:
Originally Posted by galahad05 View Post
Improper gapping, maybe.
The gap looks OK to me. No need to gap these, they come set to spec and are usually good out of the box.

Here's why the plug is a little more carbon covered than the others: the compression pressure in that cylinder was enough to result in combustion and enough expansion to prevent a detectable skip, but not high enough to result in a clean burn. Why? Because some of the compressed mixture was leaking out past the sparkplug which was not properly torqued down!
That's why you see the carbon all the way up the threads and packed under the seal.
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  #16  
Old 10-05-2012, 10:01 PM
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Ahhhhh.
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  #17  
Old 10-09-2012, 07:18 AM
kcornwell kcornwell is offline
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Thanks guys for the prompt advice. Awesome Forum!
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