The best replacement spark plugs for a 5.4L Triton are the ones matched to its cylinder heads. Our shortlist is Motorcraft SP479X for the applicable two-valve engines, SP546X for the earlier three-valve design, and SP509X for the later three-valve design. These are different applications, so the top choice for one truck can be the wrong purchase for another.
Start with the exact vehicle, engine and build information, then confirm the current part in Ford’s catalog. A listing that says only “Ford 5.4L” leaves out too much. This comparison focuses on stock applications; supercharged engines, engine swaps and replacement or repaired heads need their own verified specification.
Best 5.4L Triton spark plugs at a glance
| Pick | Best buying situation | What to check | Main limitation |
|---|---|---|---|
| Motorcraft SP479X / AGSF22WMX | Applicable two-valve 5.4L engines | Ford lists examples including 1998–2003 F-150 5.4L and 1998–2004 Expedition 5.4L; verify engine and fuel configuration | Not a substitute for the three-valve plugs or the supercharged 5.4L specification |
| Motorcraft SP546X / PZK14FX | Earlier three-valve applications calling for SP515 or SP546 | Ford identifies the SP515 replacement and black-coil-boot application; check the engine build and installed heads | 2008 model-year listings overlap with the later design |
| Motorcraft SP509X / HJFS24FPX | Later three-valve applications calling for SP509 | Ford identifies interchange with SP509 and the brown-coil-boot application | Does not replace SP546X merely because both fit some 2008 vehicles |
The application examples above come from the selected products’ Ford catalog records. They are a way to narrow the purchase, not a blanket fitment guarantee for every vehicle in a year range. The current listings for SP479X, SP546X and SP509X should be checked against your vehicle before ordering.
1. Motorcraft SP479X: first choice for the matching two-valve application
SP479X is the clearest starting point for an eligible older two-valve truck or SUV. Ford’s current product record identifies AGSF22WMX and includes the older AGSF22W, AGSF22WM and SP479 references. For a concrete manual check, the 2003 Expedition owner’s guide, page 322, specifies AGSF-22WM for its 5.4L V8.
There is an important exception within the same engine displacement: the 2003 F-150 owner’s guide, page 255, gives the normally aspirated 5.4L and the supercharged 5.4L different plug specifications. Do not extend this recommendation to a Lightning or another supercharged application.
- Why choose it: a direct Motorcraft catalog route, with legacy part references that help reconcile older service records.
- Tradeoff: the familiar SP479 name does not make it suitable for a later three-valve head.
- Buying detail: distinguish one plug from a pack of eight. An eight-plug pack is a complete count for the stock V8; order quantity one means one pack, not one plug.
The following listing is titled SP-479/AGSF22WM, and its selected product photograph shows SP-479-X and AGSF-22W-MX packaging. Confirm the part supplied and your vehicle fitment when ordering.
Motorcraft SP-479 / AGSF22WM Spark Plugs, Pack of 8
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Check the current SP479X specification with Ford.
2. Motorcraft SP546X: first choice for the earlier three-valve plug design
Choose SP546X when Ford confirms the earlier three-valve application for your installed engine. Ford identifies it as PZK14FX, states that it replaces SP515, and identifies interchange with SP546 and the black-coil-boot application. Its current catalog includes 5.4L F-150 entries for 2004–2008 and Expedition entries for 2005–2008, but the overlap year needs more than a model-year lookup.
Ford TSB 08-7-6 describes difficult spark-plug removal on specified 5.4L three-valve applications with engines built before October 9, 2007. It warns that part of the plug can remain in the cylinder head. That is an engine-build boundary for the bulletin, not permission to assume every vehicle carrying a 2008 badge has the same head or plug.
- Why choose it: Ford explicitly identifies the current SP515 replacement, reducing confusion from listings that mix old and newer numbers.
- Tradeoff: buying the correct replacement does not remove the risk involved in extracting the old plug.
- Buying detail: verify SP546X/PZK14FX itself. A title mentioning HT15, SP515 and SP546 together is not enough to establish the manufacturer and exact supplied part.
Check Motorcraft SP546X with Ford. Use the manufacturer listing to confirm the part and purchase quantity with the supplying dealer.
3. Motorcraft SP509X: first choice for the matching later three-valve application
SP509X is the choice to check when your later three-valve application calls for SP509. Ford identifies HJFS24FPX, interchange with SP509, and brown coil boots. Its current catalog includes 2008–2010 F-150 5.4L entries and 2008–2014 Navigator 5.4L entries. A correct model-year match still needs the right engine and installed head design.
The value here is straightforward part matching. SP509X is not an upgrade to install in a head designed for SP546X. Similarly, a coil-and-plug bundle adds a separate coil fitment decision and extra parts to the bill. Buy a bundle only when the diagnosis and both component specifications justify it.
- Why choose it: the current Ford part keeps the SP509 application identifiable without relying on a broad marketplace title.
- Tradeoff: brown boots are a useful catalog clue, but changed coils or replacement engines can make appearance alone misleading.
- Buying detail: confirm that the listing supplies plugs alone or the exact bundle you intended, and check its plug count.
Check Motorcraft SP509X with Ford.
How to choose without buying the wrong set
Identify the actual engine first. Record the model, model year, engine, fuel configuration and VIN. Ask about any engine or cylinder-head replacement history. The 2004 F-150 Heritage and the newer-body 2004 F-150 illustrate why the year and “5.4L” alone are insufficient: Ford lists the Heritage under SP479X and the applicable newer F-150 under SP546X.
Resolve the three-valve changeover before shopping by price. Ford’s removal bulletin identifies the engine-build information sticker on the left cam cover. Have a technician confirm the installed head and plug application if the build date, coil boots or repair history conflict. Use the current Ford service information for that engine; the historical bulletin establishes a known concern but may have later service updates.
Keep the gap and tightening instructions application-specific. Ford’s 2003 manuals direct owners to the vehicle emissions label for gap information. The 2008 F-150 guide says its 5.4L three-valve gap cannot be adjusted. The 2010 F-150 guide has its own engine specification table. A number copied from a different year or plug family should not become a universal instruction.
Budget for the complete job. Compare the delivered cost of the correct eight plugs, any genuinely needed related parts and qualified labor. Avoid paying for unrelated coils, a water pump or diagnostic tools just because a search result calls them “spark plug” products. There is no basis here for promising a horsepower gain, a fuel-economy improvement or a cure for every misfire.
Our verdict
For a stock 5.4L Triton, our preferred buying route is the exact Motorcraft application: SP479X for the eligible two-valve engine, SP546X for the confirmed earlier three-valve application, or SP509X for the confirmed later three-valve application. Choose by the verified specification first, then compare pack size, total cost and seller terms. If the engine or heads have been changed, resolve that uncertainty before buying a set.
Frequently asked questions
Do all Ford 5.4L Triton engines use the same spark plugs?
No. Two-valve and three-valve applications differ, and the three-valve engines also have an important plug-design changeover. Verify the vehicle, engine build and installed cylinder heads before choosing a part.
What is the current Motorcraft replacement for SP515?
Ford’s current SP546X listing identifies it as replacing SP515 and as interchangeable with SP546 for the applicable design. Confirm that your engine calls for that application; SP509X is a different choice.
Which spark plugs does a 2008 F-150 5.4L need?
Do not decide from the model year alone. Ford lists both SP546X and SP509X across relevant 2008 applications. Have the engine build, installed heads and current Ford application checked before ordering.
Can I use one gap and torque setting for every 5.4L?
No. Follow the exact vehicle and plug service specification. Ford’s 2003 guides refer to the vehicle emissions label for gap information, while the 2008 F-150 guide says its 5.4L three-valve plug gap cannot be adjusted.
Should I remove early three-valve plugs myself?
Ford’s removal bulletin warns that affected plugs can break and leave part in the head, and its procedures are intended for trained technicians. Arrange service with someone familiar with your exact engine and the current Ford procedure.
