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What are the best spark plugs for my Jeep Wrangler TJ 4.0?

JEEP GC

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This question comes up often, so I figured it's time for a FAQ on the matter.

The later model 4.0 engine (2000 and later) is what is known as a DIS (Distributorless Ignition System) which is far fussier about what spark plugs it likes to run well on. A DIS ignition system also fires the spark plugs twice as often which means a conventional copper-core spark plug only lasts half as long in this type of engine. All 4.0L engines that are 2000 and newer have the DIS ignition system. 1999 and older 4.0L engines aren't nearly as fussy so long as they are the right model plug. 2000 and newer 4.0L engines won't run well for long on single-tipped Platinum plugs, even though some catalogs show them as an acceptable plug. So do avoid any platinum plug that only has platinum on the center electrode.

I always recommend dual-tipped Platinum or Iridium spark plugs which will perform well for at least 100K miles. Iridium tipped plugs will last significantly longer than even the 100K miles dual-tipped platinum plugs will.

Good dual-tipped platinum plugs include the Autolite APP985 and Champion 7412 at https://www.summitracing.com/parts/cpn-7412

A great iridium tipped plug for the 4.0 engine would be the Autolite XP985. A technical trainer at I know at Autolite checked his iridium plugs at 165K miles with his company's electron scanning microscope and they showed no wear yet.

Such plugs last so long that it's a good idea to smear a tiny dab of copper-based antiseize onto their threads before screwing them into the head. Make sure no antiseize gets onto the electrodes (tip).

So while conventional plugs are what the factory installs and they are the cheapest, that doesn't mean they are the best choice for replacement spark plugs.

NOTE: 30,000 miles is the recommended spark plug service interval for conventional (non-platinum/non-iridium) spark plugs due to 2000 and newer 4.0 engines having a waste spark ignition system.
Somewhat confusing. For a 1997 4.0L TJ What plug is the best ?
 
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Jerry Bransford

Jerry Bransford

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Is there any opinion on plug wires? One better than the other? These plug wires work best with these plugs?
Avoid so-called "performance" ignition wire sets, especially any that claim "low resistance". Low resistance might sound good but it's not, resistance is actually added at extra cost to the ignition wiring and spark plugs to eliminate static and noise they generate that can be heard over AM or CB radios or cause problems for the PCM.

Stay with OEM Mopar if you can find them, or at least avoid store brands or other cheap wiring sets.
 
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BlueJay

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Hi all, old and interesting thread but still have a question because mentioned plugs are not in stock anywhere around me. They cross referenced to NGK 3459 and Autolite XP 5325. Any reason not to use either of these? Cheers
 
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Jerry Bransford

Jerry Bransford

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Hi all, old and interesting thread but still have a question because mentioned plugs are not in stock anywhere around me. They cross referenced to NGK 3459 and Autolite XP 5325. Any reason not to use either of these? Cheers
Hard to say without knowing your model year TJ and what engine you're running. You haven't completed your Profile yet which is where we normally look to see what you have. :)
 

BlueJay

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Hard to say without knowing your model year TJ and what engine you're running. You haven't completed your Profile yet which is where we normally look to see what you have. :)
Ahh ha...makes sense.. I added a few details to profile. Thanks for the nudge.
Soo.. 2000 TJ 4.0 and the supply chain is reeking havoc so I suspect these crossovers will be ok but just throwing the question out there...
Cheers
 
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Jerry Bransford

Jerry Bransford

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Ahh ha...makes sense.. I added a few details to profile. Thanks for the nudge.
Soo.. 2000 TJ 4.0 and the supply chain is reeking havoc so I suspect these crossovers will be ok but just throwing the question out there...
Cheers
The only iridium plug from Autolite I'm sure is the correct one for a 2000 4.0 is the XP-985 which is my personal preferred plug. I don't know about their XP-5325. For NGK's conventional plug I'm only aware of their ZFR5N.
 

tworley

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Longjeeprubi05

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Plugs supposedly come pre-gapped but pre-gapped for what? One gap setting is not going to be correct for every single engine it'd be the right plug for. Not to mention it is not uncommon for a boxed spark plug to be accidentally dropped before it's sold which can change its gap setting.

In my book, it's always best to spend 30 seconds on each plug before installing it to make sure its gap is correct. That can save a hard to diagnose problem later.

Hey Jerry. Thanks for info. Just got my first LJ 2005 rubi. Ohh. And I’m just down the street in st johns county.
 
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mastergunnera8

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So O'Reillys has the XP985 with two rebates...$3 per plug from autolite ($18) and $12 if you buy 4 or more from O'Reillys;

so $30 off of $57.81 ($27.81 = $4.60 per plug) for me in Va.

they also do a military discount (10%) if that applies to you...the above pricing is not with MIL

Also Autozone has the plug at $8.79 per, so there may be an additional .30 per plug price match opportunity (probably not stackable with MIL)....I'll try it out tomorrow and let everyone know...
Cheers!!

https://www.oreillyauto.com/detail/...tomotive-suv-2006-jeep-wrangler?q=xp985&pos=0
 
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