New spark plugs make a big difference!


VegasOPM

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I picked up an '06 TJ X Model a few months back. It ran fine, but seemed incredibly flat under acceleration. I wrote it off to 33" tires and 3.73 gears (which will be addressed soon). Since it had 106K on the clock, and I had no maintenance history- I'm going through the whole rig. New brakes, new tires, new fluids, AC recharge and I finally got to the plugs. They were pretty worn, but the electrodes weren't burnt off or anything like that. I switched to a set of Champion Iridium plugs and the difference is actually shocking. It runs much smoother and the acceleration is finally almost tolerable. My niece drives it to work lately and she even texted me asking what I had done to the Jeep.

Long story short, if you can't remember the last time you changed plugs or you have no idea if they've been changed- check them out. I wish I had done it months ago. $50 and 1 hour of time made a HUGE difference.
 
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Chris

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Oh yeah, don't skip out on plugs! It's one of those things that should be changed semi-regularly. They're cheap and easy to do, and can make a big difference in some cases!
 
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89grand

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That reminds me, I should do mine. I don't even have much more than 30k on my plugs, but they are over 10 yrs old.
 

fourpointzero

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Champion are the suggested OE brand, correct?

As far as 3.73’s and your 33’s, do you have an auto or manual trans? Im currently on 3.73’s w an AX-15 and have no complaints. Maybe Im just accustomed to it. I just recall when I had 29” tires, my shift points were really quick. Wasn’t a fan. Im sure had I crawled back then, it would have been more enjoyable, Id guess.


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Jerry Bransford

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Champion are the suggested OE brand, correct?
They are one good brand, I like Autolite too as the other brand.

Know that because your 2001 has the coil rail ignition system that it is fussy about what spark plugs it likes to run well on. There are three plugs I recommend for newer 4.0L engines likes yours. These first two are good for 100k miles... Champion 7412 or the Autolite APP-985. Both of those are double-tipped platinum (platinum on both sides of the gap).

Do NOT install the Champion 3034 or Autolite AP-985 in to newer coil-on-rail 4.0L engines which are single-tipped platinum plugs (which are only suitable for the older 4.0 engines with a distributor cap). Single-tipped platinum plugs will eventually cause misfires and/or a rough idle in newer coil-on-rail 4.0 engines. Single tipped means the platinum is on just one side of the gap.

Or the Autolite XP-985 which is iridium tipped. This is what I run in m '04 4.0L engine, it's good for 200k miles and it's suitable for use in any of our 4.0L or 2.5L engines.
 

dbbd1

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One of the first things I do when I get a vehicle is to change the plugs. This jeep had a gap of more than 2mm on the plugs when I got it. It still ran good though.
 

fourpointzero

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They are one good brand, I like Autolite too as the other brand.

.....Do NOT install the Champion 3034 or Autolite AP-985 in to newer coil-on-rail 4.0L engines which are single-tipped platinum plugs (which are only suitable for the older 4.0 engines with a distributor cap). Single-tipped platinum plugs will eventually cause misfires and/or a rough idle in newer coil-on-rail 4.0 engines.

Thanks again, Jerry, for chiming in with this excellent nugget of info! I’m pretty sure I installed the Champion 3040 plugs when I purchased my ‘new to me’ TJ @134k miles. Now roughly @175 K miles, I have had random rough idling, though not too bad nor often, but has always been questionable as to why. So will change them out and chime back.

I do believe my TJ also suffers from heat soak in the summer on days hotter than 90 degrees (NE). Something I was going to address by shielding the suggested injectors and adding the heat shield over the manifold. But the above mentioned random rough idle has happened in the winter on very cool days. Yet not in the same type of idle as the suspected heat soak.



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04 LJ

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They are one good brand, I like Autolite too as the other brand.

Know that because your 2001 has the coil rail ignition system that it is fussy about what spark plugs it likes to run well on. There are three plugs I recommend for newer 4.0L engines likes yours. These first two are good for 100k miles... Champion 7412 or the Autolite APP-985. Both of those are double-tipped platinum (platinum on both sides of the gap).

Do NOT install the Champion 3034 or Autolite AP-985 in to newer coil-on-rail 4.0L engines which are single-tipped platinum plugs (which are only suitable for the older 4.0 engines with a distributor cap). Single-tipped platinum plugs will eventually cause misfires and/or a rough idle in newer coil-on-rail 4.0 engines. Single tipped means the platinum is on just one side of the gap.

Or the Autolite XP-985 which is iridium tipped. This is what I run in m '04 4.0L engine, it's good for 200k miles and it's suitable for use in any of our 4.0L or 2.5L engines.
Jerry just to clarify....your second paragraph says DO NOT install....then your 3rd says or the Autolite XP-985. You are recommending the 985’s, right?
 

Jerry Bransford

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Jerry just to clarify....your second paragraph says DO NOT install....then your 3rd says or the Autolite XP-985. You are recommending the 985’s, right?
Recommendations for newer TJ 4.0L engines like yours are the Autolite APP-985, Champion 7412, or Autolite XP-985. I recommend against Autolite's AP-985 (one 'P') which only has the platinum coating on one side of the gap which causes rough idles/misfires on the newer waste-spark ignition system used on 2001 and newer 4.0L engines. The APP-985, 7412, (both platinum) and XP-985 (iridium) plugs have their coatings on both sides of the gap which is what a waste-spark ignition system needs.

Waste-spark means the spark plug is fired twice as often, the "wasted" spark being on the exhaust stroke. That newer 4.0 ignition systems fire the spark plugs twice as often as is required means the spark plugs last half as long. That's why the recommendation for platinum or iridium tipped spark plugs and not plain copper plugs on newer waste spark 4.0L engines. The waste spark is there to help reduced emissions by firing during the exhaust stroke to insure no remaining raw gasoline fumes will get out the exhaust.
 
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tony e

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Watched a youtube video about changing plugs. Suggested putting motor oil on the threads. Cant say I agree with that. Maybe some Anti-seize?