Pontiac Repair: spark plug problem, allexperts volunteers, valve seals

Question
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Hi Harold - Thanks a bunch for your answer.  I still have the original plug and upon close visual inspection I can't find any cracks or defects.  Are defects with the plug likely to be detectable or would they mostly be hidden?

I have checked the oil and it appears okay (only has 2.5K miles on it).  I will change it immediately, but should I be able to determine pretty readily if there was a blow-by problem that may have contaminated the oil and possibly damaged the bearings?

Would you recommend any diagnostic work now to check for leaky valve seals or gaskets or whatever?

On the catalytic converter, how would I know if I damaged it?  Is there some test I can do?  Our state has an annual E-check requirement.  Could this cause my car to fail the test?

I really want to make sure that I find if there is still a problem existing that caused the plug to go bad in the first place.

Mike


Followup To
Question -
Hi Harold - Thanks for your interest. This is not a Pontiac question, but I hope you can help me with your general knowledge and expertise. There were no AllExperts volunteers available for my car. I have a 2000 merc grand marquis with a 4.6l engine. 41000 miles. It has run great till the other day when the check engine light went on and the car was noticeably misfiring. I was 500 miles away from home and decided to drive home without diagnosing or fixing the problem. I had the problem diagnosed at Auto Zone as "#5 cylinder misfiring". I checked the plug and it had built up considerable spotty grayish residue. I changed the plug and after several cold start/driving cycles the light went off. Problem solved.

But I do have a couple questions that I hope you can answer for me-
1. Could I have damaged the engine by driving 500 miles with the misfire occurring

2. What may have caused the plug to go bad. These are 100K mile plugs per Ford. (I checked the #1 plug and it was okay.) What would be a logical test to find the root cause of the build up on the plug. Could there be a blown head gasket?

Thanks - Mike";

Answer -
To answer the first part of you question..It is never a good idea to keep driving the car when it is missing, especially 500 miles. It may not have done any noticeable damage to the engine right now but if the plug was not firing, the gas was still being injected into the cylinder and it would wash out all of the oil on the cylinder walls and get past the rings into the oil and then onto the bearings. Also you most certainly have done some damage to the catalytic converter. Better get the oil changed right away.
Just because Ford says that the plugs will last 100k does not mean that they wont have any problems. It could be a bad resistor inside the plug or cracked porcelain insulator.

Answer
Sometimes you can see the problem with the plug and sometimes you can't.
Just change the oil and drive the car. If you still have a problem it will show up.
Like I said before, if you have a misfire for any length of time, The gas will get passed the rings and into the oil. Also raw gas in the exhaust will cause damage to the converter. How much damage is hard to say. If the car is running ok now, leave it alone. If it fails the E Check due to a bad converter, deal with it then.