Sunday, January 16, 2011

Spark Plugs

Issue: Spark plugs loosen and then blow out, on V-10's from the late 1990's to about 2003.


My sense is the problem is quite small and occurs much more often on the V-10s produced in the late 90s. Steve Newton said he's only aware of two blown plugs among his many customers, both on the late 90s chassis. At the Ford Truck Enthusiasts forum there are a couple of surveys of the members there. They showed less than 5% had had this problem and my sense is that those threads would be skewed toward folks with the problem, who are searching for a solution and so end up there. There are some "consumer" sites where people can "sign" on-line petitions about this issue. Scanning those entries shows many more late 90s vehicles. And it is important to note that very few entries I came across on all these sites were for motorhomes or vans, but of course there are fewer of those.

Nonetheless, it seems that there clearly was a problem with either the design or assembly of this engine. The problem seems to be that are too few threads in the plug holes and on the spark plugs, apparently only about 4 threads holding these plugs in these aluminum heads on early models.

Ford made some changes over the years to address the problem but it is hard toget reliable information as to exactly what was done when and how effective it was. What is clear is that Ford eventually introduced a redesigned spark plug and increased the depth of the spark plug threads in the heads. The latter change was supposedly made for the 2003 model year but it is hard to pin down exactly when due to vagaries of the production process. For instance, my chassis was built in May, 2003 but the guy at says it may well have the older heads.

You can apparently drive more or less safely with a blown out plug, to a point of repair, for instance. Disconnect the coil pack and the corresponding fuel injector. sells an emergency kit that you can use to plug the hole, although that apparently isn't essential.


1. Ford supposedly now recommend plugs changes or at least inspection and retorque every 30K miles, instead of 100K as stated in your owner's manual.

2. Repairs can be made. Ford apparently prefers new heads - sSeveral thousand dollars. But there is ample evidence that simpler repairs are effective. All involve inserts in the damaged plug hole into which a new plug is installed. There is a Ford approved hardened aluminum insert. But there are also many reports of good results with Timeserts and with whatever does. Whatever the approach it seems wise to have the work done by someone who's done it before and has had success.

Two brothers have developed a unique tapered insert system that they can install with the head in place. They have the right tools and have done this many times.

Cleanliness is important and they clean the plug holes well before installing the new plugs. They use more torque than Ford specifies. But from all indications they get excellent results.They will also come to you, anywhere in the country. Their approach is considerably less expensive than new heads. Detailed cost info is on their Web site. I've found no evidence of problems with their approach after doing several hundred repairs.

They begin by removing the air cleaner and intake ducts down to the throttle body. Then the doghouse inside the cab. They loosen the wiring harnesses for each cylinder bank and remove some hoses. Then they remove the 10 coil units and the boots that attach them to the plugs. Then they blow out the plug holes which can accumulate considerable debris when the boots are removed. Then they remove the plugs, checking the "break loose" torque as they go. Then each plug hole is cleaned with a rotating wire brush to remove any deposits and blown out again. They check the condition of the rubber boots and may recommend new ones (I got new ones even though not really needed). They apply dielectric grease to the tips of the boots and other grease where the boots seal to the heads. New plugs are then installed and torqued to 28-32 ft/lbs
vs. the 15 or so spec'd by Ford. This is a bit controversial but they have had no problems and they believe the root cause of this problem is inadequate torque. The boots and coils are refitted and the other parts that were removed are reinstalled. Then the engine is started and checked for any codes, to verify that all is well.

The cost for this work was $400 (which includes the new plugs) plus $100 for the new boots (not really needed but I figured while we were in there, why not replace them to assure a good seal, as I've heard of some problems if water gets past the boots). That's a lot for a spark plug change but not when you see what is involved in doing one on these engines and it compares favorably with what I've heard others were charged at Ford dealers.

And there are a lot of sensitive parts at stake. Each coil unit is about $100 and could be broken in this process and there is a onnector to each coil that you don't want to break. Plus if there is damage to the plug threads noted during a change, then you need to make an insert repair.

Contributor: Terry (in Nevada)

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