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

Chris said:
Oh no, I didn't intend to come across as rude. I just meant to say that you'd probably get more attention in a new thread. Sometimes questions can get lost in these long posts :)

Admittedly I don't know the answer either, as I have coilpacks on mine.
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Chris; always the gentleman. You are an excellent moderator and have created a similar site. Thanks!

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Jerry Bransford said:
The platinum coating allows the plugs to perform well 3-4X as long as conventional spark plugs. Iridium outlasts platinum by over 100%. How much longer isn't well known yet. An electron scanning microscope saw literally no erosion on the electrodes at 165k miles in a test vehicle owned by Autolite's technical trainer who I know.

The fine-wire electrodes used in better plugs like the Autolite APP985 or XP985 also allow them to fire more reliably in difficult combustion environments.

They're better in many ways not many are aware of.
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Just ordered some autolite xp985 last night. My check engine light just came on the other day and took it to advanced to get scanned and they said Misfire in cylinder number three. But if I where to guess they haven’t been changed in a very long time so I figured this is a good choice.
 
Just curious, anyone know why Jeep didn't use dual electrode plugs? I ask because my 2002 4Runner has the same type of ignition system, with the same reputation for eating spark plugs. But the factory plugs, and anything short of Iridium aftermarket plugs, are always dual electrode.
 
WallyWest said:
Just curious, anyone know why Jeep didn't use dual electrode plugs? I ask because my 2002 4Runner has the same type of ignition system, with the same reputation for eating spark plugs. But the factory plugs, and anything short of Iridium aftermarket plugs, are always dual electrode.
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Probably because Chrysler went cheap on the factory equipment like that.
 
Tzerambo said:
Probably because Chrysler went cheap on the factory equipment like that.
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Probably because while the concept sounds good dual electrode plugs don't really help. For example of manufacturers who aren't known for going cheap, Lexus doesn't use them, neither does BMW or Mercedes. Not even Corvette comes with them. They come with iridiums and platinum plugs but not dual electrodes which many, including me, consider their value to be questionable. Personally I wouldn't pay extra for them.
 
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Jerry Bransford said:
Probably because while the concept sounds good dual electrode plugs don't really help. Lexus doesn't use them, neither does BMW or Mercedes,none of which are known for going cheap on such things. They come with iridiums and platinum plugs but not dual electrodes which many, including me, consider their value to be questionable. Personally I wouldn't pay extra for them.
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I know I payed a little extra for auto lite iridum plugs I wanted something will last longer than coper
 
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Jerry Bransford said:
Probably because while the concept sounds good dual electrode plugs don't really help. For example of manufacturers who aren't known for going cheap, Lexus doesn't use them, neither does BMW or Mercedes. Not even Corvette comes with them. They come with iridiums and platinum plugs but not dual electrodes which many, including me, consider their value to be questionable. Personally I wouldn't pay extra for them.
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Pricing isn't all that much different, I put NGK double platinum dual electrode plugs in my 4Runner for about the same as the recommended plugs for the TJ.

It's not just factory spec, the entire community for 3rd gen 4Runners say use dual electrodes or you will be sorry. The exception being if you go Iridium, but those are much more expensive and the double platinum plugs are good for at least 100k miles. I didn't try regular plugs just because the forums were full of people who had and immediately got misfires.

I would bet Lexus has used them, since they are just dressed up Toyotas and I know several Toyota engines that came with dual electrode from the factory. I don't know if anyone in the last 10 years or so even makes a waste spark engine, but if they do they probably use Iridium plugs.
 
I just installed the Bosch double iridium 9656 plugs on my 2005 TJ Rocky Mtn. Has anyone else use these, if so what are your thoughts?
 
Spark plugs are cheap and only take a few minutes to replace...don't try and reinvent the wheel. Use an OE spec plug and call it a day. More driveability problems have been caused by trying to use some whiz bang plug (that's supposed to last twice as long and costs 3 times more) than any other self induced "upgrade".

And Champion plugs are for lawnmowers.
 
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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 7034.

A good 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 and they showed no visible wear.

Such plugs last so long that it's a good idea to smear a 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.
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Three places say that the NGK7866 does not fit my vehicle. 2001 4.0.
 
I was having O2 sensor malfunction warnings and low mpg issues. Since there was a lot I could address, I chose to go with OEM plugs since they're like half the price of Iridium. Granted they last half as long, but miles/dollar they're about the same.

O2 sensor light was fixed by new cat converters. I still was getting 11 mpg which I thought was too low. Then I changed to OEM plugs and mpg went up to about 13.5 which seems right. I live on an island so I don't rack up many miles per year, therefore it will still be awhile before I have to change the plugs again.

FWIW the old plugs were Bosch with 4 tips. I think the PO was doing everything he could to fix the O2 MIL w/o changing the cat. The Jeep ran fine with them but mpg was low even though they didn't look old or worn.
 
PatMc said:
Use an OE spec plug and call it a day. More driveability problems have been caused by trying to use some whiz bang plug (that's supposed to last twice as long and costs 3 times more) than any other self induced "upgrade".
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My mechanic told me the other day that he had a technician with a TJ that swapped to iridium plugs and instantly lost 5 mpg. He dealer back to OEM copper plugs and the gas mileage went back to normal. His reasoning was that the engine was designed for use with copper plugs and the spark is different with Platinum and iridium.
 
Captain Phoenix said:
2005 LJ Rubicon with the I6.

I was asking about a preferred brand of spark plug gapping tools for used on Platinum and iridium plugs.
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The type with the two little notches cut into it used to grip/bend the electrode near its base. Nothing that touches the platinum or iridium tip. 😊
 
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NGK doesn't recommend changing the gap on plugs more than 0.008 and I don't either. If a plug is damaged in shipping it should be returned. You just can't gap a modern plug with any accuracy. The point at which the spark generates is no longer a simple gap between two big flat solid points, the shape of electrode and cathode are complex and set precisely at the factory. I'm sure some people will squak about setting the gap on all their plugs but when the people that make the things say don't do it - don't do it.

"Gapping should never be attempted on multi-ground plugs"

https://www.ngk.com/learning-center/article/185/proper-gapping-instructions
 
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