New spark plugs make a big difference!

Jerry Bransford said:
Yes the 2.4L has a waste spark design ignition system too. It does not however take the same model spark plugs the 2.5 and 4.0 engines do.

For iridium I'd go with Autolite's AI5263 and for a double-tipped platinum Autolite's APP5263. The iridium would be good for probably no less than 200k miles and the platinum about 100k miles. Both would perform the same during their lifespans.
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Okey-doke thanks for the info
 
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I have an issue that is starting to happen in the last few thousand miles where at a stop light idling the engine starts missing but then stops in a couple of seconds and runs fine. There are about 27k miles on NGK-ZFR5N PLUGS, No codes showing. Could changing to the proper iridium plug help this?
 
Those plugs are a conventional model which does not cause problems like a single-tipped platinum will. Unless your plugs are fouled, bad gap, or worn out I'd suspect something else. It wouldn't hurt to switch to something else like the Autolite XP985 iridium but...
 
I hate to disagree with Jerry, but I didn't have good luck with the XP plugs. 3 of the 4 ground electrode "buttons" disappeared creating a slight miss within a few thousand miles.

I tried NGK - not bad. Then on a whim I installed the cheap Champion Copperplus plug listed on decal under the hood - RC12ECC, (which changes up to Champion part number 438). Fits both 2.5 and 4.0 engines. Right now, my engine has never run better.
 
RaymondT said:
I hate to disagree with Jerry, but I didn't have good luck with the XP plugs. 3 of the 4 ground electrode "buttons" disappeared creating a slight miss within a few thousand miles.

I tried NGK - not bad. Then on a whim I installed the cheap Champion Copperplus plug listed on decal under the hood - RC12ECC, (which changes up to Champion part number 438). Fits both 2.5 and 4.0 engines. Right now, my engine has never run better.
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Interesting. I'm still running great with the XP plugs.
 
CharlesHS said:
This topic has been discussed ad nauseum; I am sure I will receive numerous negative comments, but here goes.
While some members recommend the iridium, some recommend the double platinum tipped and others recommend the standard plugs.
Shortly after purchasing my '01 4.0L I replaced the OLD NGK ZFR5N factory recommended plugs with the platinum tipped plugs recommended on the forum. Within less than a week my engine was throwing codes for random misfires on all cylinders. I pulled the plugs and really didn't see a problem so I went up to a friends house who was a Jeep dealership mechanic for almost 30 years.
He connected the factory diagnostic tool to the OBD2 port, revved the engine to around 1800 rpm's for 200 seconds and registered over 200 misfires on most of the spark plugs.
I told him that I had inspected the plugs and didn't see any thing obvious, but he pulled them any way. Upon pulling the first plug... he asked who put these platinum tips in; the factory recommends the ZGK ZFR5N ?
He explained to me that around 2001 the dealers were having a lot of problems with reported misfires on new vehicles along with explaining the waste spark idea and that after extensive research the factory found the problem to be the platinum plugs. Apparently a lot of vehicles have problems, but some don't.
He pulled the platinum plugs out and installed the NGK's and 95% of the misfires went away; after performing a combustion chamber cleaning the other 5% went away and the codes were gone.
Another diagnostic test was performed for 200 seconds and in that time there was only 1-2 misfires on two cylinders; I add Seafoam cleaner to my fuel once a month and the problem has not returned.
This has worked for me...
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Sadly this site is full of many people with bad advice, same for the YouTubers at times. Your comment here is pin worthy.
As a master technician myself, I pull up my software with the OEM information and just do the proper thing for many OEM maintained drivers.
My custom built stuff and heavily modified engines I do my best to keep within factory specs. The whole lubricant on the plug idea that some have expressed is definitely not recommended. Glad they fixed your issue!
 
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Interesting thread revival. I just checked and I have the Champion Copper Plus RC12EEC plugs which are a heat range of 12. Looking at the ZFR5N plugs they are heat range 5. I do have an occasional slight misfire at idle, the plugs are probably 3-4 years old with around 20K on them. Thinking of trying a set of the ZFR5N plugs.
 
Skulljeep said:
Sadly this site is full of many people with bad advice
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THIS site is absolutely NOT full of bad advice. Everybody here will give you the best advice that they can.
Two of the best and most prolific are Jerry Bransford and Mr. Blaine. If they chime in on ANY subject the best thing that you can do is pay attention. Between the two of them they have more PRACTICAL knowledge than anybody alive. Others might argue from time to time, but they've been proven right more times than you could count.
 
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I bought my 2005 TJ with 56K miles on it last October. I have a new set of iridium plugs sitting on a shelf which I am hoping to replace this weekend.
I have read here that they should be gapped at 0.035 but some said 0.040 for iridium plugs. Does it really matter?
 
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Jerry Bransford said:
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.
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So regarding the Autolite XP-985 and the Champion 7412…. What is the recommended gap for these plugs? I have a 2003 TJ sport X
 
Capt'n said:
So regarding the Autolite XP-985 and the Champion 7412…. What is the recommended gap for these plugs? I have a 2003 TJ sport X
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.035 or .040. I'd go .040 on newer TJs with the hotter/higher voltage coil rail ignition system as your 03 has.

Never gap platinum or iridium plugs with a tapered sliding gap tool which can damage the coating. Instead use a tool with a notch cut into it meant to bend the electrode to achieve the correct gap. Like this...

download-16.jpeg
 
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Jerry Bransford said:
.035 or .040. I'd go .040 on newer TJs with the hotter/higher voltage coil rail ignition system as your 03 has.

Never gap platinum or iridium plugs with a tapered sliding gap tool which can damage the coating. Instead use a tool with a notch cut into it meant to bend the electrode to achieve the correct gap. Like this...

View attachment 472567
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Just want to extend a big THANK YOU, to you Jerry and all the members on this forum. I am 60 years old, and am revisiting old wrenching skills that I haven't touched since the late 1970s when my Dad "MADE ME" work on my vehicles or I wouldn't be driving. I have received a lot of help and encouragement from you all and it has been a blessing. Cheers.
 
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I just went to get my new NGKs and went to 3 stores, got 5 plugs and had to order the 6th one for tomorrow:rolleyes: Anyway in checking the gap on one of my old Champion RC12EECs it was only .030, then I checked the gap on the new NGKs and it was also .030. I have a 2000 and a waste spark. Engine is fairly fresh at under 20,000 miles since rebuild. FSM says .035. Jerry do you think I should go with FSM of .035 or .040, or how about a loose .035?:)
 
Been driving diesels for years and I can't tell you how many years it's been since I changed spark plugs on a vehicle, I found my gappers and they are the wire type not the tapered.
 
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B1Toad said:
Been driving diesels for years and I can't tell you how many years it's been since I changed spark plugs on a vehicle, I found my gappers and they are the wire type not the tapered.
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Are feeler gauge types OK to use for iridium plugs?
Jerry Bransford said:
.035 or .040. I'd go .040 on newer TJs with the hotter/higher voltage coil rail ignition system as your 03 has.

Never gap platinum or iridium plugs with a tapered sliding gap tool which can damage the coating. Instead use a tool with a notch cut into it meant to bend the electrode to achieve the correct gap. Like this...

View attachment 472567
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Jerry,
Thank you for your reply - I will gap them at .040 for my 2005. Is a feeler gauge type OK to use for iridium plugs?
 
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