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Toyota Corolla / Chevrolet Prism Iridium Spark Plug Replacement

Updated on January 21, 2013

Denso Iridium Long Life Spark Plug

Most Toyota Corolla engines designated as the 1ZZ-FE type come standard with Denso Iridium Long Life Spark Plugs that require replacement at over 100,000 miles. If your Corolla has reached this mileage marker and you wish to replacement the plugs, this DIY article will provide the steps involved in replacement. The 1ZZ-FE engine now come with a coil pack for each plug so there is no need to consider ignition wire replacement. Denso and NGK were at one time the only provider of Iridium spark plugs. Since then, Bosch, Autolite and Champion are now providers of iridium plugs. Having experimented with these other plugs, I have noticed no difference in performance but cannot comment with respect to longevity; however, switching to platinum plugs will result in a performance and fuel economy degradation. Platinum plugs only offer longevity and cannot generate the hotter spark of an iridium plug.

If the plugs are being replaced due to engine misfire and new plugs have not resolve the problem, test each coil pack for a malfunction. The easiest way is to dis-connect the wire lead to each coil pack while the engine is running. If there's a drop in engine rpm when disconnected, it is working properly. If there is no difference in engine function, pull the coil pack and look for any corrosion on the coil pack to plug connectors. Re-connect the coil pack, start the engine and perform the test again. If there's no change, consider replacing the coil pack. Usually a bad coil pack will trigger the Check Engine light to come on.

Step 1 - Remove the Plastic Engine Shroud

Step 2 - Remove Coil Pack Electrical Connectors

Step 3 - Remove Coil Pack Bolts & Ignition Wire Harness Nuts

Step 4 - Pull Out the Coil Packs

Step 5 - Remove the Spark Plugs

Step 6 - Apply Anti-Seize to new Spark Plug Threads

Insert New Plugs

Thread each new plug and apply enough torque, via a 3/8 socket wrench, to ensure the new plug washers are seated. If unsure as to the correct torque, use a torque wrench and torque to the spark plug manufacturer's specifications. Although from my past experience plugs tend to be over-torqued, I am now experiencing plugs that have loosened. This may be mechanics being overly cautious on not stripping the threads in an aluminium headed engine. I have found that a 3/8 socket wrench provides just the right amount of leverage to apply enough torque to keep the plugs from loosening up.

Reverse the fore-mentioned steps for re-assembly after the new plug installation has been completed.


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