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4.6L & 5.4L Spark Plug Replacement Procedures

How to Replace Spark Plugs in the 4.6L & 5.4L F150


The engineers at Ford made replacing the spark plugs on the 4.6L and 5.4L engines a difficult task. Not only are the locations difficult to access, but then there's the risk of stripping the spark plug threads. However, once you've done the operation and know the tools (and variety of extensions) required to complete the task, it can be done in a reasonable amount of time. Replacing the spark plugs in your 4.6L or 5.4L V-8 will keep your engine running efficiently and at peak performance. It is generally a good idea to replace your ignition coils (coil on plugs) when performing this task, as they do wear out. Signs that your ignition system needs attention include misfire under load, hard/rough starting, poor fuel economy, and reduced performance/throttle response.


The spark plugs on the 4.6L and 5.4L engines are located in the cylinder head, towards the inner edge. The positions can be easily located because each spark plug has its own ignition coil. The spark plugs themselves are located several inches below the surface of the head, so you won't physically see them until they are removed. Spark plug changes on the 4.6L/5.4L is partially a blind operation, so pay close attention to what you are doing.

Replacement Procedures

• Disconnect the negative battery cable.
• Remove the plastic engine cover, which has 3 bolts that require a 10mm hex head.

• Unplug the ignition coil connector and fuel injector connector to gain access to the single coil hold down bolt.

• Remove the coil hold down bolt ( 1 bolt requiring a 7mm hex head). Be careful not to lose the bolt in the engine valley. This is best done by loosening the bolt with a socket, and then removing it by hand.

• Remove the ignition coil by pulling it straight up (this may require a firm tug).

• Use compressed air to blow out any debri from the cup in the cylinder head that houses the spark plug. Any dirt, dust, or grime that you don't remove can enter the cylinder when the spark plug is removed.

• Using a 5/8" spark plug socket (one with a special rubber boot inside to hold the spark plug in the socket) and the required extension(s), remove the spark plug (counterclockwise). Since you can not see inside the cup, it is recommended you secure the socket onto the plug while the extension/socket is not connected to your socket wrench. Once you've secured the spark plug in the socket, connect your wrench and loosen the spark plug. This will ensure you have a firm grip on the spark plug before you begin loosening.

• With the spark plug loosened, disconnect the wrench and remove the spark plug completely by hand.

• Apply a light coating of anti seize to the threads of your new spark plug. This will ensure future removal is smooth, as well as reduce the risk of stripping the threads of the new plug by acting as a lubricant.

• To install your new spark plug, first secure it in your spark plug socket. Plugs must be started by hand to ensure you do not strip the soft aluminum threads of the cylinder head. Spark plugs should thread smoothly and you should be able to thread them completely without the use of a socket wrench. Once the plug has been threaded into place, snug it up with a wrench. Do not overtighten. A firm "snug" is all that is necessary.

• Apply a small coating of dielectric grease to the tip of the ignition coil and then install the coil onto the plug. Reinstall the coil hold down bolt and reconnect the coil and fuel injector(s) to the wiring harness.

Tips & Tools for Replacing the Spark Plugs on the 4.6L and 5.4L V-8

• Bank 1 (passenger side):

Cylinder 4 is the most difficult plug to change. In order to increaes work space, remove the #3 coil and unplug the #3 fuel injector. You should then be able to squeeze a hand to the rear of the engine where the #4 plug is located. To remove this spark plug, we used three 6" socket extensions and a swivel/u-joint. The same setup can be used to remove the #3 spark plug. You will also need these extensions to remove the coil hold down (picture below). Replacement of the #2 and #1 spark plugs is fairly straight forward and can be done with 6" extensions.

• Bank 2 (driver side):
For cylinder #8, use a 7mm wrench instead of a socket to remove the coil hold down bolt (the fuel rail is in the way). A flexible extension can be used to remove the coil hardware on #7. The same three socket extensions and swivel/u-joint that were used on #4 can be used on the #7/8 spark plugs. The #6 spark plug is a relatively straight forward removal. In order to access the #5 plug, we removed the power steering reservoir bracket (three 8mm bolts hold it in place). With the bracket removed, the #5 plug is easily accessible.


Click any image to view full-size.

Extensions and tools used to remove spark plugs in a 4.6L or 5.4L F-150

• Here's an overview of the various extensions and flex joints that are required to access the spark plugs. Four different variations were required to complete the task.

• The red arrows in this image indicate the coil and fuel injector connectors. If you have factory ignition coils, they will be black, not red. The coils on this engine have been replaced by aftermarket ones. If you're nearing or over the 100,000 mile market and still have the factory ignition coils, replace them, as you don't want to have to repeat this task anytime soon. When the coils are worn, the engine may buck, miss, or hesitate, especially under load.


• Here is a close up view of the cup in the cylinder head where the spark plugs are located. The base of the spark plug is several inches below in the cup. Changing the spark plugs on the 4.6L and 5.4L V-8 engine is a partially blind operation, so you will have to rely on feel to ensure that everything goes smoothly. Be sure to blow the cups out with compressed air, as they have been collecting dust and debri for tens of thousands of miles.

• An assortment of hoses makes it difficult to access the number 4 cylinder (passenger side, rearmost). This image displays how we reached the spark plug with our extensions. Sometimes it is helpful to build the extensions as you go (i.e. start with a 4 inch section and your socket, attach it to the spark plug, and then attach your next extension) as opposed to trying to line up 16 inches worth of extensions at once.

• You should always support the socket with your free hand as you apply pressure to your wrench. This will keep the socket perpendicular to the spark plug nut, which minimizes the risk of stripping or breaking it off.

• As seen in this image, you will also be required to use a series of extensions and swivels in order to remove the ignition coil retaining bolts.

• The arrows in this image mark the location of the three fasteners that hold down the bracket that must be removed in order to access the number 5 cylinder.

• Two 6 inch extensions were used to easily remove the number 5 spark plug. Notice that the spark plugs are not necessarily straight up-and-down in the cylinder heads. This is why it is important to support the socket as you apply force to the rachet; keep the socket perpendicular to the spark plug.

• Close up view of removing the number 8 spark plug. Support the socket/extensions, as the fuel rail does not provide much room and you do not want to bend it.

• The number 8 cylinder also has an assortment and lines and hoses and make access difficult. As you see in the pictures, the correct combination of extensions will slide right in without having to remove any of these lines.

Additional Tips:
• The fuel injector connectors have a red gasket on the inside that tends to fall out. Make sure to reinstall the gasket, and be careful not to let one slip out of reach.
• If your spark plug will not thread, it is probably seated too far into the spark plug socket and the threads are therefore not exposed enough to reach the cup in which they sit. Pull the plug out of the socket an 1/8" to increase exposure of the tip of the spark plug and try again. Remember, all spark plugs should thread into the cylinder head with ease.
• Only use Motorcraft brand spark plugs. These are quality items you may be dissatisfied with lesser parts.
• Most spark plugs come pre-gapped, but always double check. 4.6L and 5.4L 2v engines require a gap of .054 to .056 inches. If you are gapping plugs, gap them to .055. If in doubt of what your gap should be, it is listed on the emissions label of your truck, located under the hood.
• If you manage to strip the threads in the cylinder head, have the truck towed to Ford for repair. If you have never repair a damaged thread, it is not recommended you attempt the procedure.