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The Ford Three-Valve Broken Spark Plug Blues

Jim Allen | Writer
Posted December 1, 2010

How To Avoid A Heart-Stopping Repair Bill For A Maintenance Item

If you are the owner of a Ford truck with a three-valve (3V) modular V-8 or V-10 engine built from 2004 thru 2007, you have either faced the misery of broken spark plugs-or you will. The Ford 4.6L, 5.4L or 6.8L 3V engines are some of the best and most durable engines Ford has ever built, but like Superman, they have a Kryptonite weak link. In this case, it's the OE Motorcraft spark plugs. They don't typically fail in service but often break upon replacement, leaving a piece in the cylinder head that can lead to an expensive repair.

The High-Thread (HT) Motorcraft plugs for the three-valves built through 2007 (built by Autolite and also sold under the Autolite name) are a multi-piece design. Carbon buildup inside the combustion chamber locks the lower part into place. It can take as little as 35 lb-ft to break that piece off the main body and it remains in the head. It's almost a guarantee that at least one spark plug will break. What happens after that depends on the knowledge, skill, and toolbox contents of the technician doing the job. With the right tools and knowledge, the problem is usually solvable without major pain or expense, bearing in mind that shops will charge actual time on this job. If the tech is clueless or careless, the vehicle owner can be in for a wild ride.

Early on, Ford developed a special removal tool and came out with a Technical Service Bulletin (TSB) with detailed service procedures. That original 2006 TSB has been updated several times, with the final one being TSB 08-7-6 (you can easily find it on the web). For 2008, Ford redesigned the 3V cylinder head to use a new one-piece spark plug. Unfortunately, it will not retrofit to the older heads and Motorcraft/Autolite hasn't altered the design of the 2004-07 plugs. Even though Ford specifies the use of a nickel antiseize on the tip upon replacement, there is plenty of evidence that those plugs will do the same thing in another 60,000 to 100,000 miles, at least a good portion of the time.

Because it's such an oddball spark plug, the aftermarket doesn't offer many other choices. Besides Motorcraft and Autolite, there are only Brisk and Champion. These latter two are both one-piece plugs that won't break. The Brisk plugs, however, are designed for competition; the heat ranges and construction materials may not be ideal for a stock engine in low-speed operations. Currently, that leaves Champion as your best bet. Champion was clued in right away to the problem, but it took a couple of years to come up with a design didn't get them into patent-infringement hot water.

Lisle Tools also entered the game early on with help. They looked at the Ford kit and came up with a better idea of their own, one that was much less likely to drop bits and pieces into the combustion chamber. The general consensus seems to be that, among techs that have tried both, most prefer the Lisle, saying it's easier to use and hundreds of dollars cheaper. Lisle has also managed to amass a pretty good bag of tricks in dealing with unexpected problems.

Change Now Or Later?
The owner's manual for 3V-powered trucks may list a 100,000-mile service interval for "normal" operating conditions and a 60,000-mile interval for "special" conditions. Ford defines "special" as lots of low-speed operation and city-type driving. Techs and industry professionals hint that seldom are OE sparkplugs of any type delivering optimal performance past 60,000 miles, so they recommend replacing the plugs in the 50,000- to 70,000-mile range for optimum fuel economy.

There is a not-always-apparent rhyme or reason to which 3V engines will have broken plug problems and which will not. Techs we asked have seen plugs break off at 11,000 miles and have had all eight come out at 100,000 miles. These are at the ends of a broad spectrum of experiences, and both are relatively uncommon occurrences. Generally, the earlier you do the change, the better the chances of fewer breaking off-but it's no guarantee. The consensus seems to be that most cost-effective solution is to get some miles out of the OE plugs, and then either get the Lisle tool and be ready, or find a shop that is well versed in removing the plugs. Individual owners who perform DIY changes seem to prefer getting them outta there ASAP once they learn of the problem. There's really no wrong answer if you are prepared to deal with it.


Lisle Tools
Clarinda, IA 51632
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