My daughter has a 2003 Ford Mustang with a 4.6 liter engine. The problem is one of the spark plugs has come out of it and there is no more threads to hold the spark plug in. This happened right after her boyfriend replaced the spark plugs doing a tune up because it had a miss in the engine. Now I am worried about it getting properly repaired. I have heard horror stories about these engines when this happens. What it the real story behind this repair?
What causes this problem is the spark plugs were changed and were not tightened correctly. The person who changed the spark plugs last didn’t torque them to the proper specification using a torque wrench! When this procedure is omitted the spark plugs WILL come loose, stripping out the spark plug threads. Unfortunately this engine along with the 5.4 liter engine has ONLY 4 spark plug threads to hold the spark plugs in the cylinder head. If you under tighten them or over tighten them, damage to the cylinder heads will soon follow. This is why a torque wrench is mandatory to change the spark plugs correctly so this problem won’t happen.
In order to properly repair this problem and for it to stay “fixed”, then you need to remove the cylinder head and have a spark plug inserts installed “from” the combustion chamber outward. This repair costs several hundred $$$ and customers never like this price so a lot times they choose the least expensive repair. Of course this involves putting an insert from the top of the cylinder head into the combustion chamber. This is NOT the “Best way” to repair this problem, just the least expensive way.
The success rate of doing this type repair is between 75 to 80% with a 20 to 25% failure rate because most shops are reluctant to purchase the special repair kit and procedure due to the high price that it costs.
At my shop we invested several hundred dollars for a special tool repair kit that makes the success rate of doing the repair this around 99%. But I still warn people that choose this way to repair there is a chance that it MAY not work.
If you are a gambler and most of your driving is in town, then doing this inexpensive procedure may be they way to go. If you spend a lot of time on the highway, out of town then this IS NOT the way to go. Breaking down in another city is never fun and always expensive.
Bite the bullet and fix it right the first time, it is cheaper in the long run! Or to avoid this possible problem by seeking a certified auto repair shop that will use a torque wrench to properly tighten down the spark plugs when they are changed. This way you can avoid this problem from every raising it’s ugly head.
Return to frequently asked questions