Single spark plug going bad

Tiny
THETRUTHMATTERS
  • MEMBER
  • 1999 JEEP WRANGLER TJ
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 15,000 MILES
Vehicle has a new engine and runs good, but the cylinder five spark plugs only seem to last a thousand miles. I switched the four and five cylinder fuel injector but the problem does not follow. I was also having problem with the original fuel pump and so I changed that as well. (Not as good as the original Bosch though)
Thursday, June 6th, 2019 AT 8:24 AM

5 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Hi,

Do you have a picture of one of the spark plugs that you said failed after 1,000 miles? Also, I assume you are getting a misfire, then replace the plug and the misfire is gone?

Good thinking with the injector but I am curious to see what the plug looks like after you pull it out. Thanks
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Thursday, June 6th, 2019 AT 3:14 PM
Tiny
THETRUTHMATTERS
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Thanks for your time on this. Here is one of the plugs; I pulled it out of the trash. And to answer your question, yes, I will get the engine light for cylinder five misfire (and it will idle or run rough). I change the plug and all is good. Also, with the after market fuel pump not as good as my original, I have been waiting about two seconds after turning on the ignition before I start the Jeep. Can an issue with the fuel pump have an affect on only "one" cylinder?" Thanks again.
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Friday, June 7th, 2019 AT 9:45 AM
Tiny
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If that is after 1,000 miles, that has a lot of carbon and oil residue on it. Next time you pull the plug, wipe the electrode with your fingers and see if you get any oil off of it.

I suspect you have an oil control ring issue on that piston. That would explain everything because a fuel pump as you stated would not affect just one cylinder.

Does it smoke at all when it is running? Since it is just one cylinder it is only going to be a small amount.

However, the tip being covered with oil is what is causing it to fail, so the question is where is the oil coming from? Since it is only one cylinder, the likely cause is the oil control ring.

https://www.2carpros.com/articles/blue-smoke-from-engines-exhaust
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Friday, June 7th, 2019 AT 7:11 PM
Tiny
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I was assuming (hoping) it wasn't anything internal as the engine is a re-manufactured one. New pistons, rings, valves etc. Doesn't have many miles on it. As far as smoke, I don't believe I have ever seen any, even a little. Assuming it will happen again, I will see what the spark plug looks like and get back to you. Thank you very much.
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Saturday, June 8th, 2019 AT 6:06 AM
Tiny
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Maybe keep an eye on your oil level as well. I don't it is dropping rapidly but if you mark your dipstick at your current oil level then check it periodically. It will just be another indicator but not definitive by itself because engine use oil naturally.

I will wait to hear from you. Thanks for the update.
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Saturday, June 8th, 2019 AT 8:08 AM

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