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

tjforever

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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

Thanks for the tip. Installed the XP985s today to replace the budget plugs I swapped in originally to diagnose the misfire I had when I purchased my rig. Looking forward to not changing them again for a long, long time. Easy job though!
 

MattD25

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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.
I'm sorry, disregard this reply...
I had ordered distributor parts and at first did not see the distributor/plug wires hidden under left side of valve cover. So instead of digging more like I should have, I took to this post saying mine is a 98 and doesn't have a distributor.
But it does, and idk how to delete/remove this reply. so...
 
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Redhorse

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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.

What should the gap be with the XP985 with the 2005 4L engine?
 
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Jerry Bransford

Jerry Bransford

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What should the gap be with the XP985 with the 2005 4L engine?
.035 is the official gap but the newer coil rail ignition gives so much more spark voltage that .040 is a popular/commonly used gap too.

Make sure to only adjust the gap with this type of gapping tool.

Gapping a platinum or iridium spark plug.JPG


Don't use this style with the round tapered gap adjuster which can damage the platinum or iridium coating.

Spark plug Round Gap Tool.JPG
 

Redhorse

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Redhorse

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The platinum or iridium electrode coating could be damaged if you used a tapered gap setting tool which would abrade the coating as it was slid through the electrodes to widen the gap. Like tapered edges or square loops of wire you force through the gap.

Don't use one like this on platinum or iridium plugs...

View attachment 12607


Gap setting tools with a notch cut into them that grabs the electrode next to where it is welded to the threaded area can bend the electrode up or down without damaging the coating.

Use one like this on any type plug including platinum or iridium...

View attachment 12608

So what should the spark plug gap be on the Autolite
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.

so what should the spark plug gap be on the Autolite XP985 be set at in my 2005 TJ 4.0 liter engine?
 

Redhorse

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.035 is the official gap but the newer coil rail ignition gives so much more spark voltage that .040 is a popular/commonly used gap too.

Make sure to only adjust the gap with this type of gapping tool.

View attachment 376705

Don't use this style with the round tapered gap adjuster which can damage the platinum or iridium coating.

View attachment 376707

Thank you Jerry
 
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interface

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quick question - what size plug socket will I need? I could look it up but I've found this thread very useful and I'm sure someone else might have the same question at some point. First post!

edit: I think it's 5/8, which is the only size that my son hasn't stolen lol.
 
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inkedrose

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