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BrokenSockets
April 24th, 2015, 11:28
Is there any reason that RS12YC would not be a suitable plug to use in the 4.0?

Trumbo
April 24th, 2015, 22:05
If you got a coil pack waste ignition you use NGK.

md21722
April 25th, 2015, 09:34
NGK is not necessary for a coil pack engine.

Here's some information from Champion that lists specs on both the 401 and 412 plug:

http://www.federalmogulmp.com/en-US/Technical/Documents/Champion%20Spark%20Plug%20Copper%20Plus%20Heat%20R ange%20Chart.pdf

I run the 412 in both my 1997 and 2001 and have not had any issues that I know about.

Sidewinder CC
April 26th, 2015, 05:01
Is there any reason that RS12YC would not be a suitable plug to use in the 4.0?

RS is a tapered seat plug. The RC is a gasket seat plug. You need a gasket seat.

Use RC12LYC.

In '99 Chrysler switched to the RC12ECC (double Copper) plug when the coil rail was introduced.

RC12ECC is a hair hotter than the RC12LYC plug.

The RC12LYC plugs were used from '93 to '98'

http://i519.photobucket.com/albums/u354/khinks01-02/Engine%20Work/LYC%20and%20ECC%20Plugs.jpg

Sidewinder CC
April 26th, 2015, 06:11
.Here's a spark plug application chart:

http://i519.photobucket.com/albums/u354/khinks01-02/Engine%20Work/Jeep%20XJ%20Spark%20Plug%20Application%20-%20Copy.jpg

ehall
April 26th, 2015, 07:43
where does that info come from? wonder why 99 is in the 00/01 category

Sidewinder CC
April 26th, 2015, 07:53
where does that info come from? wonder why 99 is in the 00/01 category

The data comes from the Champion and NGK websites.

In '99 Chrysler introduced the RC12ECC plugs for their coil rail 4.0's (Grand Cherokee '99) and simply made them applicable to the '99 XJ as well, even though it was still a distributor 4.0.

If you look at the Emissions decal on your firewall you'll see RC12ECC plugs listed.

ehall
April 26th, 2015, 08:10
99 ignition is same as 98 ignition, if they change the reference info for inventory control convenience then the technical difference is moot

md21722
April 26th, 2015, 11:21
I don't think there's any downside to running the double platinum in a 4.0 with a distributor. Come to think of it, I think I run Champion 438's in my 2001. I used to run the Truck & SUV plug when they were available.

BrokenSockets
April 26th, 2015, 22:48
Thanks for the info on the plugs - I picked up a set of rc12lyc today.
I figured out that the 6 rs12yc are actually for my Benz e320. Just got mixed up onto the shelves full of xj parts and scraps. Also sorry for not being specific that this was a question for a 96.