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Any spark plug gurus?

tchase

NAXJA Forum User
Ok... So it's time for a tune-up on the old XJ.

Wondering if anyone can offer any advice regarding what plugs to run and/or what the difference is between the 2 different plugs that are spec'd.

I have an '85 with a 2.5L long-block from an '02 Wrangler. Manifolds, fuel, and ignition systems are stock(ish) '85.

The OE plug for the '85 is Champion RFN14LY
The OE plug for the '02 is Champion RC12ECC

Do these 2 plugs physically interchange? My gut says go with the '02 plug as I'm sure it will physically fit but I really don't know much about plugs.
 
Since RFN14LY are available, that is what you should use.
 
Bascially identical except the RFN14LY is a hotter plug (14 versus 12). I suspect the 02 ECM runs things a touch leaner and hence needs a "colder" plug.? If in doubt, I would go with the colder RC12ECC plug as too hot can cause detonation and potential damage versus too cold just fouling the plug.

https://www.sparkplugs.com/product.aspx?zpid=8592 (RFN14LY)
https://www.sparkplugs.com/product.aspx?zpid=8519 (RC12ECC)

Perfect! Exactly the info I was hoping for. Thanks so much.
 
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