http://www.fordproblems.com/trends/triton-spark-plug-ejection/ - you can look up fixes for this with helicoil repair kits.
The head casting may be thin at the #7 plug.
This article is worth reading ---- http://blog.wiseautotools.com/ford- spark-plug-blow-out-solved/
DO NOT use a helicoil. Use a Timesert which is the only Ford approved repair.
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