#5 spark plug literally burnt a hole through. What's the cause?

Asked by Apr 09, 2015 at 12:04 AM about the 1999 Jeep Grand Cherokee Laredo 4WD

Question type: Maintenance & Repair

1999 Jeep Grand Cherokee, 4.0 V6 (Laredo)
Did a tune up, replaced spark plug, spark plug rail and fuel injectors. Ran fine for about
60 miles and then check engine light came on, lost pressure.

1 Answer

Had the same problem with a 64 Saab 2-stroke - the spark plug literally burned a hole through the top of the piston. The plug was way too high heat range. For many years, I kept the piston with the spark plug sitting in the hole it had burned,

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