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Over the years many routine car maintenance and repair tasks have remained practically unchanged from a technical point of view in that if you’ve done it many times before on one model, the same procedure can be used on other models…usually.
However, over time even the most routine car and truck maintenance tasks do change enough to the point if you do it the old way, you might be doing it wrong and could possibly damage your engine or cause it to run rougher than it should.
Ford Changed Its Spark Plug Design and Replacement Procedures
That was the take-home message of a recent FordTechMakuloco YouTube channel episode where the host demonstrates how to replace the spark plugs on 2021 and newer Ford F-150 models equipped with the 3.5L EcoBoost Engine.
Related article: Older Ford (2017-2021 Ford F-150 3.5L GTDI Ecoboost Engine) Spark Plug Replacement Demo
In recent models of the Ford F-150, you are technically required to buy only Ford manufacture spark plugs due to their move toward using indexed spark plugs for additional power and fuel economy. What this means to DIY Ford truck owners is that not only will you have to buy and use Ford OEM spark plugs, but also get used to varying some on how the new style indexed spark plugs are installed.
What Are Indexed Spark Plugs?
Previously, indexed spark plugs belonged within the domain of car enthusiasts/racing professionals and their high-performance or racing engines. The term "indexed" refers to the practice of aligning the ground electrode of the spark plug in a particular orientation within the combustion chamber. The benefit of doing this is that it reputedly optimizes the ignition process and improves engine performance.
Key points about indexed spark plugs includes:
Spark Electrode Orientation: The ground electrode of the indexed spark plug is machined to match the threads of the spark plug with the threads of the cylinder head in order to orient the electrode in a specific direction—Often towards the intake valve or a particular spot in the combustion chamber to achieve a more efficient combustion process.
The Performance Benefits: Indexed spark plugs oriented properly can lead to better flame propagation and thereby, more complete combustion. The end result is potentially increased power output, improved fuel efficiency, and reduced emissions.
Special Installation Procedure: Indexed spark plugs typically involve using washers or shims to adjust the plug's position. As a check on positioning, mechanics often mark the spark plugs to ensure they are oriented correctly when installed.
Indexed Spark Plug Applications: Indexed spark plugs were once most commonly used in high-performance, racing, or modified engines. Today, they are on the road toward becoming commonly used in standard, everyday vehicles.
Special Considerations of Trial and Error: Achieving the ideal indexing for each cylinder may require some trial and error, as the optimal orientation can vary based on the engine design and other factors. While this is typically beyond the pay grade of DIY mechanics, we can expect car manufacturers going this route to provide detailed installation instructions and other aids. Finding a current repair manual for your particular model is recommended.
How to Change Indexed Spark Plugs on Your Ford Truck
For an excellent discussion about indexed spark plugs and how to change them on a modern Ford truck with the 3.5L EcoBoost engine, follow along with the host in the video below as he shows how to DIY this special spark plug change step-by-step to ensure you are doing it the right way and not the old school way you may be more familiar with.
2021+ Ford F-150 3.5L EcoBoost Spark Plug Replacement
An Important Limitation of Indexed Spark Plugs
It bears mentioning that one important limitation of indexed spark plugs for the DIY Ford owner is that because the cylinder head spark plug hole threads and spark plug threads must match exactly, any damage to the cylinder head threads will likely result in having to replace the cylinder head due to repairing a damaged thread is unlikely possible. I.E., there is not and likely will not be a Helicoil-type threaded insert option any time soon, which many mechanics rely on to fix damaged threaded spark plug holes.
Recent Used Ford Truck Shopper Warning
An extension of the above limitation is that shoppers of recent used models of Ford trucks with indexed spark plugs will need to ascertain that the spark plug cylinder head holes are not damaged and the reason why a seller might be quick to unload a future repair problem onto an unsuspecting buyer.
As always, a prepurchase inspection by a qualified mechanic can alert you to any potential problems such as this.
For additional articles related to Ford truck repairs and maintenance, here are a few recommended useful ones for your consideration.
- Fatal Flaw of This Ford Truck Engine Rescued from a Dealership Fail
- Common Mistake Ford Truck Owners Make Upgrading Their Engine
- The New Ford DIY Repair Manual Every Ford Owner Should Have
Timothy Boyer is an automotive reporter based in Cincinnati. Experienced with early car restorations, he regularly restores older vehicles with engine modifications for improved performance. Follow Tim on Twitter at @TimBoyerWrites for daily news and topics related to new and used cars and trucks.
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