Spark plug indexing

What is spark plug indexing?

On some late model engines equipped with gasoline direct injection, it’s important for the open end of the spark plug’s ground electrode to not be directly facing either the fuel injector or the intake valve.

Once fully torqued, the open section of the spark plug, where the center electrode can be seen, will be within the center of a 45° range of the injector and intake valve. This final positioning allows for “high ignitability.”

How to install a spark plug in an index-designed engine

At the present time (Spring 2023), the following manufacturers require spark plug indexing in some of their engines:

• Automotive: Mercedes Benz, Land Rover, Jaguar, Nissan/Infiniti, and Freightliner
• Non-Auto: Ski-Doo Snowmobiles w/E Tech Engines

The cylinder head spark plug threads and the recommended spark plugs have their threads oriented so the spark plug is properly indexed when installed to specification using a torque wrench.

1) Start threading the spark plug by hand using the proper spark plug socket
2)Then tighten to spec using a calibrated torque wrench.

Do not use an air or battery powered ratchet to install spark plugs, especially in an index-designed engine.

Remember, when properly installed the open end of the spark plug should be facing the GDI fuel injector and the intake valve. The only way to accomplish this orientation is to use a torque wrench.

Also, never install a non-indexed spark plug in these applications.

©, 2023 Rick Muscoplat

Posted on April 12, 2023 by Rick Muscoplat