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

mastergunnera8 said:

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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Jerry Bransford said:

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.

Click to expand...

Jerry Bransford said:

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.

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Jerry Bransford said:

.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

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Jerry Bransford said:

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

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Jerry Bransford said:

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.

Click to expand...

Jerry Bransford said:

.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

Click to expand...

Jerry Bransford said:

.040 is a popular/commonly used gap too.

Click to expand...

Jerry Bransford said:

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.

Click to expand...

Jerry Bransford said:

Definitely.

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Chris said:

That was my thought as well. Iron and steel shouldn't be an issue.

I'm curious to see though if this solves your issue.

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Mike_H said:

So...an Update. I posted about the OEM NGK plugs in the second post of this thread. Seems Jerry has left us for the time being, but I'm going to pull the trigger on new plugs. I've been getting misfire codes on my CEL basically since I put the NGK plugs in. I've tried a couple of different things, like swapping plugs and injectors to see if the trouble follows. I've also cleaned the throttle body and IAC (actually removed them). Its worst when the engine is cold, which leads me to think that the plugs may be the culprit. Warm engines ignite easier as the fuel is atomized better. Once I'm warmed up, she runs pretty good, and fairly smooth. I'm thinking my plug don't have enough "zapp" when the engine is cold to get that whole reaction to kick off. A double tipped iridium or something might help get more energy down there where I need it.

Also...Jerry mentioned Copper based anti-Seize. Copper only, or would Aluminum work?

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Nickster said:

That's right!! Copper anti seize is the very best on the spark plugs on all 4.oL motors!!

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Offwidth said:

Best antiseize is nickel based. Bostic nuclear-grade NGBT-8 Never-Seez is the way.

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