4.0L '04 uses different spark plug than '99-'03?? - JeepForum.com
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post #1 of 3 Old 05-28-2020, 06:07 PM Thread Starter
MN Ben
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4.0L '04 uses different spark plug than '99-'03??

While changing spark plugs, I looked in my Haynes to verify the plug gap and noticed the '04 calls for NGK ZFR5N with a .040 gap. The years '99 to '03 call for Champion RC12ECC with a .035.
Now some may say that either will work for my '04 4.0L WJ, but when it comes to electrical components, I like to use what was installed at the factory.
I am wondering why there is a difference in plugs when be 2004 engine came out.
Any idea? As I could not find one when doing a search.

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post #2 of 3 Old 05-28-2020, 06:24 PM
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Yes, in 04 (possibly later runs of '03), Jeep switched to NGK V-power ZF5RN. That's what I always run in mine since it was OEM, haven't had any issues. Pretty sure it retains .035 gap, however. I've read several posts/articles stating the NGK idle quieter than the Champion and had minor power improvement, but that's all subjective and seat-of-the-pants.

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post #3 of 3 Old 05-28-2020, 08:25 PM
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The NGK ZFR5N is what the 2004 4.0 runs, the flash programming for the ignition drivers is optimal with a 0.036 gap.
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