DRocK2000XJ

Thank you kindly sir.

NewJerseyXJ609

In my experience... The fancy Dancy plugs work like crap in a 4.0.

Stick to oem champions for the best results.

jtm01xj

See ive had different results in mine with champion plugs i went with ngks got better results then went to e3s and got even better results even my smog test results were better with e3s

salad

So you couldn't pass smog test and your Jeep ran like crap with normal plugs? Pro tip: The problem ain't the plugs.

Basic copper plugs are the only reliable performer in a 4.0. Champions were installed from the factory, later on Chrysler issued a TSB that superseded them with NGKs. Champion part numbers being something like RC9YCC, RC12LYC, RC12ECC, etc. The real one will be under the hood on a sticker. Lots of seasoned Jeep vets run NGK ZFR5N (replaced the RC12ECC) with fantastic results.

Aside from heat range issues and dubious claims about performance and fuel economy there's a big reason you should keep fancy plugs out of your Jeep: they're too damn expensive! In an engine like the 4.0 - especially in an XJ which implies that the newest factory one is about 12 years old - you WANT to inspect and change them regularly. Blowby will gunk them up, and you will be able to catch lean issues before your fancy $15 plug explodes and destroys your piston and valves.

cjfrigo

Alright thanks I just keep getting different answers on the 2000 xj I was getting 14 mpg and i ran seafoam threw my jeep part in gas part threw vacuum now I'm around 18 big jump? Anyways going to change the plugs. Sorry for butting in your post gasouthernxj

jtm01xj

I never said anything about not passing a smog test i pass every time i just got cleaner results withe the e3s then ngks or champion plugs and the ngks that you stated i had in mine but when it came time to change them i put in the e3s and 10k later they still are working great for me and i do regular maintenance on my jeep and its always up to par

Cherokeekid4x4

I'm not taking sides or anything, I'm also no mechanic but there are a lot of things on our jeep that came factory that we replace with all sorts of s@@@ now. Injectors being agood example. People run injectors from a car. Why can't we run e3's? What proof does anyone have proving that they aren't any good? And don't say because it came factory. Mine came with a factorymuffler (duh) so should I replace it with the exact type!? Lol I'm just saying e3's are good plugs, I haven't heard a bad thing about them. They are just newish so everyone's kinda staying back. But if they work for him great! And I'm sold on getting some. I have champions in mine right now and I can't say that they are the greatest.. Also a mechanic told me today he ran the Bosch (fancy ones) and had a very good experience.

Cherokeekid4x4

All that being said and after looking at reviews on numerous vehicles and motors. Mainly 4.0 motors I'm seeing mixed things but mainly good things. It seems the vehicles that they don't do we'll in are people who like to be aggressive with their motor. Run different fuel..etc. I'm having a similar problem to the OP. slow acceleration and poor mileage (8mpg) so ill be waiting to see some more comments on this. Like I said I run champions. Been in there for almost a year, maybe I should check them lol

Aljay

e3s are a joke ! I worked at orielly auto parts I would not sell them. They can cause issues like some have said. I had a well known engine builder in my store often (Hans Fuestal ) I asked him about them he laughed and said they are a gimick .

salad

Try doing a search on this site for problems with E3s or Bosch +4s. Generally rough-running, lack of power, and premature fouling are the issues. You can experiment if you like but don't expect good results...

It's not really an OEM vs. After Market issue btw. Some of those plugs simply aren't in the correct heat range, or the original plugs were able to handle a wide variety of situations where one 4.0 that was within spec ran great with some fancy plugs, yet another 4.0 that was ALSO within spec didn't. It's an old, sloppy engine. You can't really compare that to something that actually exceeds specs, or where such a specification is irrelevant (eg. muffler)

RTorrez1

These are all the problem that I had when I had them in my 98 4.0. Plus they are way over priced.

NewJerseyXJ609

Same problems here.

There isn't anything better than regular old champions.. Ngk is a quality plug as well I've just always got the Champions..

mitch500

I run E3's no issues in the past 10,000 miles. Idle is smooth, acceleration is smooth. I have champ coppers in my Girlfriends xj and they work fine too. Although my jeep feels faster but that may be in my head..

Aljay

Anyone remember split fires ...................? Well if they were that great maybe you would hear about them still.

Jesse Hallum

OEM-spec plugs provide the best performance. Our 2001 Sport specs Champion 438 Copper Spark plugs. NGK Copper Plugs are also OEM-spec for some earlier models. Consult your Owner's Manual for the correct OEM spec spark plug to use for your Jeep. It's that simple.

Oversized tires will destroy fuel mileage and stress the entire drivetrain beyond OEM specs. I use only OEM tire/rim sizes. Again, consult your Owner's Manual for the correct tire/rim size to use with your Jeep. Yes, it's that simple.