Guide to Spark Plug Replacement in a Lexus LS 400 V8

by Tony Oldhand
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spark plug image by Yali Shi from

Replacing spark plugs in a Lexus can be accomplished by most do-it-yourself mechanics. While not difficult, some steps should be followed to ensure that the task progresses smoothly. Having the correct tools on hand is a requirement, as are having the correct plugs and the correct torque setting for your model year of Lexus. By taking your time and working methodically, the job is easily accomplished.

Plan the Job

First and foremost, you must plan the job. This involves having the correct size spark plug socket, an extension for you ratchet wrench, and other tools to remove and replace the engine covers. At the very least, you should have a complete socket set, screwdrivers, pliers and a torque wrench. If you feel the job is more involved then the level of tools you have on hand, refer this job to a qualified Lexus mechanic.

Safety Precautions

Safety precautions must be observed whenever you work on a car. Lexus technicians recommend that you disconnect the battery's negative terminal when changing plugs and wrap it with a cloth. Furthermore, the car should be parked on a flat surface so it doesn't roll. The transmission should be set in "Park" and the emergency brake engaged.

Accessing the Plugs

The spark plugs are below cover plates and other engine parts. To get at them, you must remove several of these parts. Keep a mental note of the dissembling process, since re-assembly is in the reverse order. You can ask a friend to record the process with a camcorder, so you can refer back to the video for re-assembly.

Replace One Plug at a Time

After all the components are removed, you should see the spark plug and ignition wires at the top of the heads. Remove the ignition wire and replace the spark plug one at a time. That way, the wires do not get jumbled. When removing the wires, do not pull directly on the wire, since this will break the internal conductors. Rather, pull on the rubber boot attached to the spark plug. Special pliers are available to grasp the boot, but not the wire.

Correct Torque

You must place the correct torque on the new spark plug. Torque refers to how tight you should tighten down the plug. This will depend on the year of your Lexus, so contact your local Lexus dealer for the correct torque setting for your car. Use the torque wrench to tighten down the plugs. Never try to guess at it, since over-tightening a spark plug will strip the threads in the head. If this happens, the head will have to be removed and a machine shop will have to repair the stripped thread.

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