What causes a spark plug to blow out on Ford 4.6 5.4 and 6.8 liter engines and how can it be repaired without replacing the cylinder head?

Answer 1

If it was installed properly, it is the threads in the head and they need to be repaired or the head replaced.

This can also be repaired by installing a TIME-SERT found on the website link below the answer. (TIME-SERT specializes in thread repair related problems.)

In addition to replacement spark plugs blowing out, there has been many original Ford spark plugs that have blown out that were in the engine when the vehicles were new. I don't believe that the spark plugs were installed incorrectly from the factory. I know that Ford has had a problem with spark plugs blowing out of their 4.6, 5.4 and 6.8 Triton engines, I think it is a design issue (4 aluminum threads holding the plugs). The heads are aluminum as well as the spark plug threads. The dealers want to replace the heads, although there is a way to repair them and make the threads even stronger, see the tech article on Ford Spark Plug Blow-out at DenLors. The repair inserts in this tech article is a thick repair insert that can be used when thin repair inserts have failed. The outside diameter measurement of the Calvan 389-100 thread insert is .73" which is a much beefier repair insert than competing brands. And the 389-100 has the correct taper, to seal the compression properly and the same part number spark plugs are used. Why risk using a thin wire insert like the guy that has his van all torn apart in the YouTube Video, when a superior repair kit is available that can be used to install much more substantial repair inserts. And a word of caution, if replacing the cylinder heads with rebuilt ones... You could be purchasing a rebuilt head with an inferior thin wire insert so be cautious if that's the route you choose.

Actually, spark plugs have and continue to blow (explode) out of the aluminum heads even when the plugs were installed new at the Ford factory. Additionally, inserts are prone to blowing (exploding) out the aluminum head too. Go to YouTube and search "FORD TRITON BLOWN SPARK PLUGS" and see a video of a Triton having blown it's second plug (an insert that didn't hold) and also "Google" a search for blown plugs (or ejected plugs) Ford Triton.

On one ocassion, a Ford Triton caught on fire when the spark plug blew out of the aluminum head, ruptured a fuel rail just above it (the plug was still sparking at the time of the ejection) and the truck was completely lost in the resulting fire. This particular event occurred in a F150 truck, having the original factory installed spark plugs.

Some evidence also suggests that the failure rate is more excessive at spark plugs located on the rear of the engine and problematic on the right rear passenger side. Some speculation also reveals that the ejection rate is higher during warm summer seasons than during winter.

Possibly, adding a ram air duct from the front of the vehicle to the rear of the engine (in the area of the rear spark plugs) may help address this issue, but this seems to be a band-aid approach to a faulty designed aluminum head, allowing only 4 threads to hold the spark plug inside the spark plug boss.